β-Trefoil fold. Patterns of structure and sequence in the Kunitz inhibitors interleukins-1β and 1α and fibroblast growth factors

摘要: Abstract Previous crystallographic analyses of the Kunitz inhibitors from soybean, Erythrina caffra and wheat, interleukins-1β 1α acidic basic fibroblast growth factors have shown that they contain a most unusual fold. It is formed by six two-stranded hairpins. Three these form barrel structure other three are in triangular array caps barrel. The arrangement secondary structures gives molecules pseudo 3-fold axis. Although different proteins very similar structures, many their sequences no significant similarities overall. structural determinants this fold described discussed paper. barrels same geometrical features: strands tilted at 56 ° to axis; diameter 16 A, β-sheet hydrogen bonded so it staggered with shear number 12. These features fit McLachlan's equations for ideal β-sheets. wide filled layers residues that, while not identical proteins, are, almost all cases, large. hairpins determined coiling packing hairpin against each interior major sequence requirements large or medium hydrophobic resiudes 18 buried sites. In total volume 3000(±120) A 3 . polyhedron model protein architecture used demonstrate main, particular symmetrical, arise equal hairpins, modified only slightly bonds between