Sequence‐specific 1H‐NMR assignment and secondary structure of the Tyr41 → His mutant of the single‐stranded DNA binding protein, gene V protein, encoded by the filamentous bacteriophage M13

Abstract

Sequence‐specific 1H‐NMR assignments are reported for the Tyr41 → His (Y41H) mutant of the single‐stranded DNA binding protein, encoded by gene V of the filamentous bacteriophage M13 (GVP). The mutant protein was chosen for this purpose because it exhibits significantly improved solubility characteristics over wild‐type GVP [Folkers et al. (1991) Eur. J. Biochem. 200, 139–148]. The secondary structure elements present in the protein are deduced from a qualitative interpretation of the nuclear Overhauser enhancement spectra and amide exchange data. The protein is entirely composed of antiparallel β‐structure. It is shown that identical structural elements are present in wild‐type GVP. Previously, we have demonstrated that the secondary structure of the β‐loop, encompassing residues 13–31 which is present in GVP in solution, deviates from that proposed for the same amino acid sequence on the basis of X‐ray diffraction data [van Duynhoven et al. (1990) FEBS Lett. 261, 1–4]. Now that we have arrived at a complete description of the secondary structure of the protein in solution, other deviations with respect to the crystallographically determined structure became apparent as well. The N‐terminal part of the protein is, in solution, part of a triple‐stranded β‐sheet while, in the crystal, it is an extended strand pointing away from the bulk of the protein dimer. One of the antiparallel β‐sheets in the protein which had been designated earlier as the complex loop has, in the solution structure, a different pairwise arrangement of the residues in its respective β‐ladders. Residues 30 and 48 are opposite to one another in the solution structure while in the crystal structure residues 32 and 48 are paired. A similar observation is made for the so‐called dyad domain of the protein of which the β‐sheet in the solution structure is shifted by one residue with respect to that of the crystal structure. Copyright © 1991, Wiley Blackwell. All rights reserved