H-1-NMR STUDIES OF THE MERCURIC ION-BINDING PROTEIN MERP - SEQUENTIALASSIGNMENT, SECONDARY STRUCTURE AND GLOBAL FOLD OF OXIDIZED MERP

The oxidized form of the mercuric ion binding protein MerP has been st udied by two-dimensional NMR. MerP, which is a periplasmic water-solub le protein with 72 amino acids, is involved in the detoxification of m ercuric ions in bacteria with resistance against mercury. The mercuric ions in the periplasmic space are first scavenged by the MerP protein , then transported into the cytoplasm by the membrane-bound transport protein MerT, and finally reduced to elementary (nontoxic) mercury by the enzyme mercuric reductase. In this work, the H-1 NMR spectrum of o xidized MerP (closed disulfide bridge) has been assigned by using homo nuclear 2D NMR techniques. The secondary structure and global fold hav e been inferred from the nuclear Overhauser effect (NOE) data. The sec ondary structure comprises four beta-strands and two alpha-helices, in the order beta1alpha1beta2beta3alpha2beta4. The protein folds into an antiparallel beta-sheet, beta2beta3beta1beta4, with the two antiparal lel helices on one side of the sheet. The folding topology is similar to that of acylphosphatase, the activation domain of porcine pancreati c procarboxypeptidase B, the DNA-binding domain of bovine papillomavir us-1 E2 and the RNA-binding domains of the U1 snRNP A and hnRNP C prot eins. However, there is no structural similarity between MerP and othe r bacterial periplasmic binding proteins.