Role of the tyrosine corner motif in the stability of neocarzinostatin

Although the immunoglobulin-like ß-sandwich fold hasno specifically conserved function, some common structural featureshave been observed, in particular a structural motif, the tyrosinecorner. Such a motif was described in neocarzinostatin (NCS),a bacterial protein the structure of which is very similar tothat of the immunoglobulin domain. Compared with the other ß-sheetproteins, the NCS ‘tyrosine corner’ presents non-standardstructural features. To investigate the role of this motif inthe NCS structure and stability, we studied the properties ofa mutant where the H bond interaction had been eliminated byreplacing the tyrosine with a phenylalanine. This mutation costs4.0 kcal/mol showing that the NCS ‘tyrosine corner’is involved in protein stability as in the other Greek key proteins.This destabilization is accompanied by remote structural effects,including modification of the binding properties, suggestingan increase in the internal flexibility of the protein. Witha view to using this protein for drug targeting, these resultsalong with those obtained previously allow us to define clearlythe limitations of the modifications that can be performed onthis scaffold. Received December 3, 2002; revised June 6, 2003; accepted September 3, 2003.