The crystal structure of outer surface protein A (OspA) from Borrelia burgdorferi contains a single-layer beta-sheet connecting the N- and C-terminal globular domains. The central beta-sheet consists largely of polar amino acids and it is solvent-exposed on both faces, which so far appears to be unique among known protein structures. We have accomplished nearly complete backbone H, C and N and C beta/H beta assignments of OspA (28 kDa) using standard triple resonance techniques without perdeuteration. This was made possible by recording spectra at a high temperature (45 degrees C). The chemical shift index and 15N T1/T2 ratios show that both the secondary structure and the global conformation of OspA in solution are similar to the crystal structure, suggesting that the unique central beta-sheet is fairly rigid.