A STABLE SINGLE-LAYER BETA-SHEET WITHOUT A HYDROPHOBIC CORE

Outer surface protein A from the Lyme disease spirochete Borrelia burg dorferi contains a single-layer beta-sheet connecting the N- and C-ter minal globular domains. The central beta-sheet consists largely of pol ar amino acids and is solvent-exposed on both faces, which so far appe ars to be unique among known protein structures. We show that the sing le-layer beta-sheet segment is surprisingly stable (Delta G for hydrog en exchange is similar to 8 kcal mol(-1) at 45 degrees C). Possible fa ctors contributing to the stability of the single-layer beta-sheet are discussed based on an analysis of the crystal structure.