Hemolytic lectin CEL-III heptamerizes via a large structural transition from ?-helices to a ?-barrel during the transmembrane pore formation process.

ABSTRACT: CEL-III is a hemolytic lectin isolated from the sea cucumber Cucumaria echinata. This lectin is composed of two carbohydrate-binding domains (domains 1 and 2) and one oligomerization domain (domain 3). After binding to the cell surface carbohydrate chains through domains 1 and 2, domain 3 self-associates to form transmembrane pores, leading to cell lysis or death, which resembles other pore-forming toxins of diverse organisms. To elucidate the pore formation mechanism of CEL-III, the crystal structure of the CEL-III oligomer was determined. The CEL-III oligomer has a heptameric structure with a long ?-barrel as a transmembrane pore. This ?-barrel is composed of 14 ?-strands resulting from a large structural transition of ?-helices accommodated in the interface between domains 1 and 2 and domain 3 in the monomeric structure, suggesting that the dissociation of these ?-helices triggered their structural transition into a ?-barrel. After heptamerization, domains 1 and 2 form a flat ring, in which all carbohydrate-binding sites remain bound to cell surface carbohydrate chains, stabilizing the transmembrane ?-barrel in a position perpendicular to the plane of the lipid bilayer.

SUBMITTER: Unno H 

PROVIDER: S-EPMC4007468 | biostudies-literature | 2014 May

REPOSITORIES: biostudies-literature