Analysis of Three-Dimensional Structure with Subunit Mismatch Arrangements of Staphylococcal γ-hemolysin Heteroheptameric Transmembrane Pore
Abstract: Staphylococcal γ-hemolysin (Hlg) consists of two separate proteins, Hlg1 (34kDa) and Hlg2 (32kDa), which lyses cooperatively mammalian erythrocytes. We have been studied pore-forming nature and assembly of Hlg on the membrane and revealed that Hlg1 and Hlg2 assemble alternately to form heteroheptameric transmembrane pores with subunit stoichiometries of 3:4 and 4:3. However, the three-dimentional (3-D) structure of Hlg pore complex has not been clarified yet. In this study, our aim is reconstruction of 3-D structure of the pore having a characteristic molecular arrangement in asymmetrical heteroheptamer, based on high-resolution electron transmission miscroscopic (TEM) images.
The shapes and sizes of subunit in the pore were measured on the basis of TEM image and the 3-D structure was constructed with computer-aided design software. As a result, it is estimated the pore forms a cylindrical structure in a superior region and funnel-shaped structure in an inferior region. That is, seven subunits bend to inside at the bottom of superior region and small cylindrical pore structure acting as functional transmembrane pore is attached. Additionally, it is revealed that several subunits are arranged out of order from vertexes of regular heptagon and largest mismatch subunit angle against the regular heptagon reachs approximately 15 degree.
Key words: Staphylococcal γ-hemolysin, heteroheptameric transmembrane pore, high-resolution negative TEM image, 3-D structure construction, molecular arrangement analysis