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    lcolumbus
    Putative function of TM1224: N-acetylmannosamine repressor Not a Kinase: When compared to a human N-acetylmannosamine kinase containing ‘bound’ ADP (PDB 3EO3), the TM1224 structure does not exhibit conservation of the ADP-binding residues. Specifically, the conserved threonine residue (T417) of the ATP-binding motif that hydrogen bonds to the gamma phosphate of the ATP molecule in kinases is replaced by an aspartate residue in TM1224 (D85). The introduction of a negative charge at this position suggests that ATP binding is unlikely due to repulsion of negative charges between aspartate and the ATP's polyphosphate tail. However, TM1224 does have a typical DNA-binding domain within the N-terminal HTH-motif. Cumulatively, analysis of the structural data leads to the hypothesis that TM1224 is solely a repressor protein, rather than a dual function repressor / kinase. Sugar Specificity: Comparison of the human N-acetylmannosamine kinase structure (PDB 3EO3) to the structure of TM1224 indicates that N-acetylmannosamine (NAM) would be the preferred substrate, rather than N-acetylglucosamine (NAG). All NAM-binding site residues (N184, D185, E232, E248) are conserved between NAM kinase and TM1224 indicating that NAM may be the preferred substrate. Therefore, TM1224 likely binds NAM as a repressor molecule that regulates DNA binding rather than as a phosphate acceptor (in a kinase reaction). BioLEd Contributors: Joseph Breheny, Kanishk Jain, Jennifer Patterson, Jaewoong Jang, Paulinder Mann, Hung Pham, Karthik Shastri, Songserea Wood, Kathryne Wren, Cameron Mura, Carol Price, Linda Columbus. Funded by NSF DUE 1044858.

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