ENGINEERING OF BETABELLIN-15D - A 64-RESIDUE BETA-SHEET PROTEIN THAT FORMS LONG NARROW MULTIMERIC FIBRILS

The betabellin target structure is a beta-sandwich protein consisting of two 32 residue beta-sheets packed against one another by interactio n of their hydrophobic faces. The 32 residue chain of betabellin-15S ( HSLTAKIpkLTFSWphTYTCAV pkYTAKVSH, where p = DPro, k = DLys, and h = DH is) did not fold in water at pH 6.5.Air oxidation of betabellin-15S pr ovided betabellin-15D, the 64 residue disulfide bridged two-chain mole cule, which also remained unfolded in water at pH 6.5. By circular dic hroic spectropolarimetry, the extent of beta structure observed for be tabellin-15D increased with the pH and ionic strength of the solution and the betabellin-15D concentration. By electron microscopy, in 5.0 m M MOPS and 0.25 hi NaCl at pH 6.9, betabellin-15D formed long narrow m ultimeric fibrils. A molecular model was constructed to show that the dimensions of these betabellin-15D fibrils are consistent with a singl e row of P-sandwich molecules joined by multiple intersheet H-bonds.