Kalata B1

Kalata B1 structure is defined by cyclic backbone (N-to-C peptide bond) combined with three disulfide bonds where two disulfides and the backbone form a ring through which the third disulfide threads, the cystine knot. This topology creates an exceptionally rigid, compact structure that resists mechanical and chemical denaturation, enzymatic degradation, and extreme pH. The result is a peptide that survives boiling, acid treatment, and all classes of proteases intact.

Kalata B1 disrupts lipid bilayers by binding to phosphatidylethanolamine headgroups (PE-specific) through its hydrophobic patch and inserting into membranes to form pores. The PE selectivity differs from most AMPs that target anionic lipids, giving kalata B1 distinct membrane targeting. The uterotonic effect is mediated by membrane disruption of uterine smooth muscle cells and may involve oxytocin receptor-independent mechanisms.

Cyclotide loops can be replaced with bioactive sequences from other peptide drugs while the cyclic cystine knot scaffold maintains structural integrity. Grafted cyclotides carrying bradykinin B1 antagonist sequences, alpha-msh/" class="wiki-internal-link">melanocortin sequences, and VEGF-inhibiting sequences have been produced with oral stability and serum half-lives orders of magnitude greater than the original peptide drugs. This platform approach represents a potential breakthrough for delivering peptide drugs orally.

Native kalata B1 and engineered variants show cytotoxicity against cancer cell lines and HIV inhibition at micromolar concentrations. The anti-HIV mechanism involves direct membrane disruption of viral envelopes. While native kalata B1 is cytotoxic, grafted variants with reduced native activity but retaining scaffold stability are being engineered as cancer-targeted drug delivery agents.