LDTI — Blutegel-Tryptase-Inhibitor
A miniature inhibitor that penetrates the tryptase tetramer pore
Zuletzt aktualisiert: June 18, 2026
Mechanismus-Haftungsausschluss
LDTI (Leech-Derived Tryptase Inhibitor) is a remarkably small Proteinase inhibitor that exploits its compact size to access a target inaccessible to all natural plasma Protease-Inhibitoren. Mast cell tryptase — a tetrameric serine protease — arranges its four active sites facing inward around a narrow central pore. Large inhibitors wie z. B. α1-Proteinase inhibitor (52 kDa), antithrombin III (58 kDa), and C1 inhibitor (105 kDa) are physically excluded. At only 4,340 Da, LDTI is small enough to penetrate this pore and engage the active sites directly.
Molekulare Eigenschaften
| Isoform | Molekulargewicht | Structural Family | Homology |
|---|---|---|---|
| LDTI-A, LDTI-B | 4.340 Da | Nicht-klassischer Kazal-Typ | 55 % auf Bdellin B3 |
| LDTI-C | 4.738 Da | Nicht-klassischer Kazal-Typ | 55 % auf Bdellin B3 |
Mechanismus der Tryptase-Hemmung
Größenabhängiger Zugang
Mast cell tryptase exists as a ring-shaped tetramer with four active sites oriented toward a narrow central pore (~3 nm diameter). LDTI's compact 4.3 kDa size allows it to enter this pore and inhibit tryptase with Ki = 1.4 nM. All natural human plasma Protease-Inhibitoren (α1-PI, AT-III, C1-INH) are too large to penetrate this pore.
N-Terminal Residue Specificity
The critical determinant for tryptase inhibition lies in the N-terminal residues. LDTI exhibits Lys1-Lys2 (positively charged), which facilitates entry into the negatively charged tryptase pore. Bdellin B3, despite 55% homology, has Asp1-Thr2 and cannot inhibit tryptase — demonstrating that two residues determine functional divergence.
Ingenieurmäßig entwickelte Varianten
Engineering der Thrombin-hemmenden Aktivität
The compact LDTI scaffold wurde engineered to acquire neuartig inhibitory specificities. Variants designated 2T and 5T were created with substitutions at the reactive site loop:
Variant 2T
Moderate thrombin inhibition. Retains partial tryptase activity. Demonstrates proof of principle for LDTI scaffold engineering.
Variant 5T
Ki = 2.0 nM for thrombin. Acquired potent thrombin-inhibitory activity through reactive site loop redesign, demonstrating the plasticity of the Kazal-type scaffold.
Additional Biological Activities
HIV-1-Replikationshemmung
Auerswald et al. (1994) demonstrated that LDTI inhibits HIV-1 replication at 20 μM concentration. The mechanism likely involves protease inhibition at viral processing steps. Although not pursued clinically, this finding highlights the broad-spectrum serine protease activity of the LDTI scaffold.
Antiproliferative Effekte
Rekombinant LDTI (r-LDTI) inhibits keratinocyte and fibroblast proliferation at picomolar concentrations. This activity is mediated through tryptase inhibition, as Mastzell-Tryptase is a potent mitogen for sowohl cell types. Relevant to fibrotic and hyperproliferative skin conditions.
Klinische Relevanz
Mast cell tryptase is a validated therapeutic target in mehrere inflammatory and fibrotic conditions. LDTI represents a natural proof-of-concept for small-molecule tryptase inhibition.
Asthma
Tryptase treibt Bronchokonstriktion an
Lungenfibrose
Tryptase fördert Fibroblasten-Proliferation
Rheumatoide Arthritis
Synoviale Mastzell-Degranulation
Psoriasis
Tryptase-getriebene Keratinozyten-Proliferation
Verwandte Ressourcen
Eglins b/c
Elastase- und Cathepsin-G-Inhibitoren.
Antiinflammatorische Mechanismen
SDS modulation of inflammatory pathways.
Verbindungsreferenz
Vollständige Datenbank bioaktiver SDS-Komponenten.
Compound Coverage Map
LDTI and tryptase inhibitors in the 107-entry leech compound catalogue.
Research Roadmap
Engineered LDTI variants and the leech tryptase-inhibitor pipeline.