A simple method to adjust inconsistently referenced 13C and 15N chemical shift assignments of proteins

Inconsistent C-13 and N-15 chemical shift referencing is a continuing problem associated with protein chemical shift assignments deposited in BioMagResBank ( BMRB). Here we describe a simple and robust approach that can quantitatively determine the C-13 and N-15 referencing of sets solely from chemical shift assignment data and independently of 3D coordinate data. This novel structure-independent approach permitted the assessment and determination of C-13 and N-15 reference of sets for all protein entries deposited in the BMRB. Tests on 452 proteins with known 3D structures show that this structure-independent approach yields C-13 and N-15 referencing of sets that exhibit excellent agreement with those calculated on the basis of 3D structures. Furthermore, this protocol appears to improve the accuracy of chemical shift-derived secondary structural identification, and has been formally incorporated into a computer program called PSSI (http://www.pronmr.com).