Dramatic and concerted conformational changes enable rhodocetin to block ?2?1 integrin selectively.

ABSTRACT: The collagen binding integrin ?2?1 plays a crucial role in hemostasis, fibrosis, and cancer progression amongst others. It is specifically inhibited by rhodocetin (RC), a C-type lectin-related protein (CLRP) found in Malayan pit viper (Calloselasma rhodostoma) venom. The structure of RC alone reveals a heterotetramer arranged as an ?? and ?? subunit in a cruciform shape. RC specifically binds to the collagen binding A-domain of the integrin ?2 subunit, thereby blocking collagen-induced platelet aggregation. However, until now, the molecular basis for this interaction has remained unclear. Here, we present the molecular structure of the RC??-?2A complex solved to 3.0 Å resolution. Our findings show that RC undergoes a dramatic structural reorganization upon binding to ?2?1 integrin. Besides the release of the nonbinding RC?? tandem, the RC? subunit interacts with loop 2 of the ?2A domain as result of a dramatic conformational change. The RC? subunit contacts the integrin ?2A domain in the "closed" conformation through its helix C. Combined with epitope-mapped antibodies, conformationally locked ?2A domain mutants, point mutations within the ?2A loop 2, and chemical modifications of the purified toxin protein, this molecular structure of RC??-?2A complex explains the inhibitory mechanism and specificity of RC for ?2?1 integrin.

SUBMITTER: Eble JA 

PROVIDER: S-EPMC5509089 | biostudies-literature | 2017 Jul

REPOSITORIES: biostudies-literature