Metalloproteases have long been recognised as key virulence factors in bacterial pathogens. By cleaving the protein scaffolds that hold tissues together, these enzymes help bacteria breach epithelial barriers, disseminate through the bloodstream and colonise new niches within the host. Proteolytic activity has been detected in pathogenic Leptospira before: secreted proteases from L. interrogans have been shown to degrade extracellular matrix and plasma proteins, and a metalloprotease called Leptolysin, a member of the pappalysin family, was recently described with broad-spectrum activity against host targets. Other Leptospira proteases have been implicated in cleaving complement proteins, a strategy that helps the spirochaetes evade the innate immune response. What has been missing, however, is detailed biochemical information about individual enzymes, particularly members of the M23 family, which in most bacteria are known primarily as peptidoglycan hydrolases involved in cell wall remodelling.

LIC11568 caught the researchers’ attention because of its unusual domain architecture. Bioinformatic analysis using resources such as InterPro and Pfam confirmed the previously reported presence of an M23 metallopeptidase domain alongside a LysM motif, a widely distributed module that binds peptidoglycan and related glycans. The team’s predictions went a step further, identifying an N-terminal signal peptide, the molecular postal code that directs proteins to the secretory pathway. Taken together, these features suggested a protein that could be exported to the bacterial surface or beyond, where it might encounter host tissue components. The M23 fold is a striking example of structural economy: a single protein fold that has been recruited for functions ranging from bacterial cell wall turnover to, as this study now suggests, the degradation of mammalian collagen.

Getting enough of the protein to study experimentally proved to be the first major hurdle. The researchers initially attempted to produce recombinant LIC11568 in Escherichia coli, the workhorse of protein expression laboratories worldwide. Under the conditions tested, however, no detectable protein appeared on SDS-PAGE gels, a frustrating but familiar outcome for proteins that are toxic to their bacterial hosts, difficult to fold, or prone to degradation. Rather than abandon the project, the team turned to cell-free protein synthesis, a technique in which transcription and translation are carried out in a test tube using cellular extracts stripped of their own genomes. Because the method bypasses living cells entirely, it sidesteps problems of toxicity and allows direct control over the reaction environment. Cell-free systems have matured considerably since their early days and are now routinely used for proteins that resist conventional expression, and LIC11568 proved to be a textbook case.

With soluble recombinant protein in hand, the researchers confirmed its identity using matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry, or MALDI-TOF peptide mass fingerprinting. This technique digests a protein into peptides and measures the precise masses of the resulting fragments, generating a fingerprint that can be matched against theoretical digests of known sequences. The match supported that the product of the cell-free reaction was indeed LIC11568, clearing the way for the functional experiments that form the heart of the study.

Those experiments delivered the study’s headline finding: LIC11568 degrades Type I collagen in a time-dependent manner. Collagen is not an easy substrate. Its triple-helical structure, stabilised by tight packing of glycine-rich chains, resists most proteases and gives skin, tendon, bone and connective tissue their remarkable tensile strength. Enzymes capable of cleaving it, collectively known as collagenolytic proteases, are relatively rare among bacteria and are strongly associated with tissue-invasive pathogens such as Vibrio species. The Leptospira enzyme showed maximum activity after five hours of incubation at pH 8.0 and 37 degrees Celsius, conditions that mirror the neutral to slightly alkaline environment of mammalian body fluids at physiological temperature. Activity also increased with enzyme concentration, consistent with a genuine enzymatic reaction rather than a contaminating artefact.

The clearest evidence for the enzyme’s mechanistic class came from inhibitor and rescue experiments. The chelating agent 1,10-phenanthroline, which sequesters divalent metal ions from the active site of metalloproteases, strongly inhibited collagen degradation. When the researchers added zinc ions back to the inhibited reaction, activity was restored. Calcium ions, by contrast, failed to rescue activity on their own, indicating that the catalytic metal is specifically zinc rather than any available divalent cation. This pattern of inhibition and metal-dependent rescue is a classic signature of zinc-dependent metalloproteases and firmly places LIC11568’s collagenolytic behaviour within that mechanistic family under the conditions tested.

The significance of the finding lies in what it suggests about leptospiral pathogenesis. During infection, L. interrogans must cross tissue barriers, survive in the bloodstream and ultimately colonise organs such as the kidney and liver. An enzyme that can digest Type I collagen would, in principle, help the spirochaete tunnel through the dense connective tissue matrices that stand in its way. The combination of a signal peptide, a LysM binding module and a catalytic M23 domain paints a coherent picture of a protein positioned at the interface between the bacterium and its host environment. The authors are careful, appropriately, to frame the result as identifying collagen as a substrate in vitro, and they note that the work provides a basis for further investigation of the enzyme’s substrate specificity and its potential role in extracellular matrix interactions during infection. Whether LIC11568 is secreted in vivo, how much it contributes to virulence relative to other Leptospira proteases, and whether it can serve as a vaccine or drug target are questions that remain open.

Methodologically, the study also offers a useful lesson for the broader protease research community. The successful use of cell-free protein synthesis after conventional expression failed demonstrates a practical route to characterising difficult Leptospira proteins, many of which may share the expression problems that plagued LIC11568 in E. coli. As the leptospirosis research field works to fill the gaps in its virulence atlas, an area that reviewers have repeatedly described as underexplored compared with other bacterial pathogens, approaches that decouple protein production from living cells are likely to become increasingly valuable. Each newly characterised enzyme, in turn, narrows the search space for interventions. If LIC11568 or its relatives prove essential for tissue invasion, inhibitors modelled on 1,10-phenanthroline’s mechanism of metal chelation, or antibodies raised against the enzyme, could one day complement the vaccines and antibiotics that currently form the limited arsenal against this globally distributed disease.

Subject of Research: Biochemical characterisation of the zinc-dependent M23 metalloprotease LIC11568 from Leptospira interrogans and its collagenolytic activity

Article Title: Expression and functional characterisation of the zinc-dependent metalloprotease LIC11568 from Leptospira interrogans reveals collagenolytic activity

Article References: Merrin, S. B., & Ramya, M. (2026). Expression and functional characterisation of the zinc-dependent metalloprotease LIC11568 from Leptospira interrogans reveals collagenolytic activity. Molecular Biology Reports, 53(1), Article 1685. https://doi.org/10.1007/s11033-026-12887-4

Image Credits: AI Generated

DOI: 10.1007/s11033-026-12887-4

Keywords: Leptospira interrogans, leptospirosis, metalloprotease, M23 metallopeptidase, collagenolysis, Type I collagen, zinc-dependent enzyme, extracellular matrix, virulence factor, cell-free protein synthesis, MALDI-TOF, signal peptide

Biofilms are structured communities of bacteria encased in a self-produced matrix of proteins, extracellular DNA, and polysaccharides. Within these fortresses, pathogens become dramatically more tolerant of antibiotics and immune attack, which is why biofilms complicate the treatment of cystic fibrosis lungs, chronic wounds, medical implants, and catheter-associated infections. Pseudomonas aeruginosa and Staphylococcus aureus are flagship biofilm builders, and both appear on global lists of antibiotic-resistant priority pathogens. An enzyme that can chew through the proteinaceous scaffolding of a biofilm, or disrupt the physiology of the cells inside it, therefore represents a genuinely different therapeutic strategy: rather than killing bacteria outright, it dismantles the architecture that makes them so hard to eradicate.

Serratiopeptidase, sometimes marketed as serrapeptase, is an extracellular protease naturally secreted by Serratia marcescens. It has been used for decades, particularly in Japan and India, as an anti-inflammatory and anti-edema agent, and earlier studies have hinted that it can affect Pseudomonas physiology and biofilm integrity. What has been missing is a rigorous, quantitative characterization of a purified preparation, since crude enzyme mixtures make it impossible to attribute activity to a single protein. The new study addressed this gap with a four-step purification pipeline: precipitation, dialysis, ion-exchange chromatography, and gel filtration chromatography, which together yielded a 15.91-fold increase in purity, sufficient for reliable biochemical and kinetic analysis.

With the purified enzyme in hand, the team determined its molecular weight to be approximately 47 kilodaltons, consistent with the serralysin-like metalloproteases produced by Serratia species. The enzyme displayed broad substrate specificity but showed its highest affinity toward casein, a milk protein commonly used as a benchmark substrate in protease assays. Activity peaked at pH 7 and 40 degrees Celsius, close to physiological conditions, and the enzyme proved remarkably durable under these optima, retaining 89.2 percent and 82.4 percent of its activity, respectively, after 60 minutes of incubation. That combination of neutral pH preference and moderate temperature optimum is exactly what one would want in a therapeutic protein intended to function inside the human body.

The kinetic analysis revealed an enzyme of impressive catalytic power. The Michaelis constant, Km, was 0.034 millimolar, equivalent to 842 micrograms per milliliter, indicating tight substrate binding, while the maximum velocity, Vmax, reached 738.2 units per milliliter. The turnover number, kcat, came in at 55.3 per second, meaning each enzyme molecule processes more than 55 substrate molecules every second. Dividing kcat by Km yields a catalytic efficiency of 1.64 × 10⁶ per molar per second, a figure that places this serratiopeptidase firmly in the category of highly efficient catalysts. For a protein being considered as a drug candidate, such numbers matter: an efficient enzyme can deliver biological effects at lower doses, reducing cost and potential side effects.

Equally informative was the enzyme’s response to chemical modulators. Metal ions including zinc, cobalt, barium, and manganese enhanced activity, as did the non-ionic detergent Tween-20 and the reducing agent beta-mercaptoethanol. Conversely, EDTA, a chelator that strips away metal cofactors, and PMSF, a classic serine protease inhibitor, both shut the enzyme down. This dual sensitivity is diagnostic: it confirms that the SP6 enzyme is a serine-metalloprotease, a hybrid classification consistent with the serralysin family, in which a catalytic serine operates within a metal-dependent active site. Knowing this helps predict how the enzyme will behave in complex biological environments and informs strategies for stabilizing it in formulation.

Perhaps the most clinically relevant findings concern stability and resistance to degradation. The enzyme retained 61.31 percent of its activity after 60 days of storage at 4 degrees Celsius, a refrigerated shelf life that simplifies handling and distribution. More strikingly, it resisted digestion by trypsin and by human serum, with in vitro half-lives of 4 and 5 hours, respectively. Therapeutic proteins typically face rapid destruction by circulating proteases and serum components, so a bacterial enzyme that survives hours in serum-like conditions is unusual and valuable. The authors note that extending the half-lives of therapeutic proteins is a major focus of drug development, and intrinsic resistance to proteolysis gives this enzyme a head start.

The anti-biofilm experiments delivered the study’s headline result. Against Pseudomonas aeruginosa MTCC 2453, serratiopeptidase achieved a maximum biofilm inhibition of 41.65 percent at a concentration of 200 micrograms per milliliter, with an IC50 of 56.92 plus or minus 8 micrograms per milliliter. Against Staphylococcus aureus MTCC 1430, the maximum inhibition was 21.87 percent at the same dose, with an IC50 of 124.6 plus or minus 8 micrograms per milliliter. The authors are careful to define these IC50 values relative to the normalized response range, meaning they correspond to 50 percent of the observed inhibitory effect rather than absolute halving of biofilm mass, a methodological honesty that strengthens the credibility of the data. The stronger effect against Pseudomonas aligns with earlier reports that serratiopeptidase alters the physiology of Pseudomonas isolates from cystic fibrosis patients and disrupts Pseudomonas biofilms and functional amyloids.

What makes these numbers exciting is not that the enzyme obliterates biofilms on its own, but that partial disruption is often enough to restore the vulnerability of embedded bacteria. Anti-biofilm agents are increasingly viewed as adjuncts: by loosening or thinning the matrix, they allow antibiotics and immune cells to reach cells that would otherwise remain sheltered. A 41.65 percent reduction in Pseudomonas biofilm formation, achieved by a single enzyme at a modest concentration, could meaningfully amplify the efficacy of co-administered antimicrobials. The enzyme’s activity at neutral pH and 40 degrees Celsius, its serum stability, and its resistance to trypsin all support the plausibility of such combination approaches.

Significant hurdles remain before serratiopeptidase reaches the clinic as an anti-biofilm drug. The current work used a partially purified preparation, and further purification, scale-up of production, formulation studies, toxicity testing, and ultimately animal and clinical trials will be required. The enzyme’s origin from Serratia marcescens, an opportunistic pathogen itself, raises production and safety questions that recombinant expression systems, which have already been used to produce serratiopeptidase in cell-free platforms, could help resolve. Nevertheless, by systematically documenting the enzyme’s molecular weight, kinetics, inhibitor profile, storage stability, serum resistance, and anti-biofilm potency, Kumar and Bhattacharya have transformed a supplement-shelf enzyme into a well-characterized candidate for rational development. As antibiotic resistance continues to erode the effectiveness of conventional drugs, enzymes that dismantle bacterial fortresses rather than merely poisoning the bacteria inside them may prove to be one of the most important weapons in the next generation of anti-infective therapy.

Subject of Research: Biochemical characterization and anti-biofilm activity of serratiopeptidase from Serratia marcescens SP6

Article Title: Elucidation of the biochemical properties of a partially purified Serratia marcescens SP6 serratiopeptidase with anti-biofilm efficacy

Article References: Kumar, S., & Bhattacharya, S. (2026). Elucidation of the biochemical properties of a partially purified Serratia marcescens SP6 serratiopeptidase with anti-biofilm efficacy. 3 Biotech, 16(10), Article 433. https://doi.org/10.1007/s13205-026-05063-9

Image Credits: AI Generated

DOI: 10.1007/s13205-026-05063-9

Keywords: serratiopeptidase, Serratia marcescens, biofilm, Pseudomonas aeruginosa, Staphylococcus aureus, protease, enzyme kinetics, antibiotic resistance, metalloprotease, anti-biofilm therapy, protein purification, therapeutic enzymes