Rossman fold

Each subunit of the homotetrameric PFK of Escherichia coli comprises 320 amino acids arranged in two domains, one large and one smaller, both of which have an rx/p structure reminiscent of the Rossman fold (Figure 6.25). 

Figure 2-27 depicts topology diagrams for the Rossman fold and for two related families of proteins. These families bind the nucleotides called GTP and ATP, respectively. Both are structural relatives of NAD. A major part of the structure of all of the proteins in these families consist of P-a units, each one containing a P strand followed by a helix. They are... 

MIPS crystal structure is characterized by a homotetrameric association, with a 222 symmetry where two monomers are related by a non crystallographic twofold axis in an asymmetric unit and two such molecules are related by a crystallographic two-fold axis at one end. The holoenzyme seems to have three well defined domains, where the N and C terminal ends are a part of the central domain which is involved in subunit interactions, an NAD binding domain containing a modified Rossman fold and a catalytic domain which contains the active site amino acids and residues that occur at the tetrameriza-tion interface (Jin et al., 2004 Majumder et al., 2003 Stein and Geiger, 2002). 

CMP-3-(i )-fluoro-NeuNAc, has been solved. The overall structure of the monomer showed only one Rossman fold (nucleotide binding domain), with the rest of the molecule showing signs of disorder it resembled GTA more than GTB, but with marked differences from the standard GTA fold. This is not surprising as the glycosyl donor is a monophosphate, not a diphosphate. 

T. maritima ASPDH revealed the presence of a dimer with each subunit composed of two domains, the N-terminal Rossman fold domain with bound NAD-cofactor and a C-terminal (a 4- (3) domain. A recently published 3D structure of ASPDH from A.fulpdus suggested that the substrate binding (mimicked by the bound citrate molecule) occurs in the C-terminal domain. It is accompanied by a substantial movement of the two surface loops, bringing the substrate into close proximity with the NAD cofactor." ... 

The first 3D structure of the E. coli NadD enzyme revealed a version of the dinucleotide-binding (Rossman) fold composed of the central seven-stranded /3-sheet surrounded by a-helices. The mechanism of NadD catalysis is likely similar to other nucleotidyltransferases of this class, including a nucleophilic attack of the 5 -phosphoryl group of NaMN on the a-phosphate of ATP facilitated by Mg " " that is coordinated by a conserved (HXGH) segment. A high-resolution 3D structure of NadD complexed with its NaAD product provided a basis for the interpretation of its strict preference for NaMN substrate over NMN. A comparison with the 3D structure of the human PNAT (see below) confirmed an anticipated overall similarity but also revealed sufficient differences in the active site area to allow for the development of selective NadD inhibitors. This conjecture was confirmed by our recent studies that allowed us to develop potent NadD inhibitors that have almost no effect on the enzymatic activity of the human PNAT enzymes (L. Sorci et al, unpublished). 

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