Bdellins A/B
Dual-family proteinase inhibitors with exceptional neurotrophic potency
Mechanism Disclaimer
Bdellins comprise two structurally distinct groups of proteinase inhibitors isolated from whole-body extracts of Hirudo medicinalis. Despite sharing protease targets (trypsin, plasmin, acrosin), Group A and Group B belong to entirely different structural families — a remarkable example of convergent functional evolution within a single organism.
Classification and Structure
| Property | Group A (Bdellastatin) | Group B (Bdellin B3) | HMW Bdellin B |
|---|---|---|---|
| Molecular weight | 6,300 Da (59 aa) | 5,000 Da | 20,000 Da |
| Structural family | Antistasin family | Non-classical Kazal-type | Kazal-type (extended) |
| Disulfide bonds | 5 S-S bonds | 3 S-S bonds | Multiple |
| Homology | 29% to antistasin | 55% to LDTI | Extended C-terminal domain |
| Reactive site | P1 Lys34 | Canonical Kazal loop | Kazal loop + membrane binding |
Bdellin B3 spans only 37 amino acids between its first and last cysteine residues, making it among the shortest Kazal-type inhibitors known. The high-molecular-weight bdellin B (20 kDa) features an extended C-terminal domain that is presumed to be involved in binding to cell membranes.
Inhibitory Specificity
Trypsin
Ki below 0.1 nM (<10⁻¹⁰ M) for bdellin B-3 and HMW bdellin; group A (bdellastasin) inhibits trypsin in the nanomolar range. Biological function: modulates trypsin activity in the leech intestinal canal, where Aeromonas symbionts secrete exo- and endopeptidases that mediate blood digestion.
Plasmin
Ki < 0.1 nM (< 10^-10 M for bdellin B-3 and high-molecular-weight bdellin B). Bdellins are present in the leech foregut (crop), where a role in preserving the stored blood has been proposed.
Acrosin
Acrosin is a trypsin-like serine protease from sperm acrosome. Bdellin inhibition of acrosin reflects the broad-spectrum anti-trypsin activity rather than a specific reproductive biological function of the leech.
Neurotrophic Activity
Neurotrophic Activity Among the Bdellins
Bdellin B
EAI increase at 0.05 ng/mL — among tested SGS components in chick embryo dorsal root ganglia (Chapter 7).
Bdellastatin
Also reported to stimulate neurite outgrowth in explant culture at low concentrations (Chalisova et al., 2003), alongside its trypsin/plasmin-inhibitory activity.
EAI = Explant Area Index, a standardized measure of neurite outgrowth from dorsal root ganglia explants.
Recombinant Production and Applications
Recombinant Bdellastatin
Moser et al. (1998) achieved heterologous expression of bdellastatin in Saccharomyces cerevisiae (yeast). Yields were 29 mg/l, and the recombinant protein was identical to native bdellastasin by mass spectrometry, circular dichroism, sequence determination and inhibition characteristics.
Anti-Inflammatory Potential
By inhibiting trypsin-like proteases at sub-nanomolar concentrations, bdellins contribute to the suppression of tissue degradation during inflammatory responses. Their dual anti-inflammatory and neurotrophic activities suggest multifunctional therapeutic potential in neuroinflammatory conditions.
Related Resources
LDTI
Leech-derived tryptase inhibitor — mast cell protease regulation.
Eglins b/c
Elastase and cathepsin G inhibitors.
Neurotrophic Effects
SGS components that stimulate neurite outgrowth.
Compound Reference
Complete SGS bioactive component database.
Compound Coverage Map
Bdellins and the leech protease-inhibitor family in the 200-compound catalogue.