Structural studies of antigen 85A and antigen 85C from Mycobacterium tuberculosis /
The antigen 85 complex, comprised of three secreted proteins: antigens 85A, B, and C, is a major protein component of the Mycobacterium tuberculosis cell wall. These 3 homologous proteins all possess a mycolyltransferase activity required for the biogenesis of trehalose dimycolate (cord factor) and...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
2001.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=725922131&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | The antigen 85 complex, comprised of three secreted proteins: antigens 85A, B, and C, is a major protein component of the Mycobacterium tuberculosis cell wall. These 3 homologous proteins all possess a mycolyltransferase activity required for the biogenesis of trehalose dimycolate (cord factor) and the covalent attachment of mycolic acids to the mycobacterium cell wall. Additionally, an interaction between the antigen 85 proteins and human fibronectin stimulates complement mediated phagocytosis by monocyte-derived macrophages, which is the first step of host infection. The crystal structure of recombinant antigen 85C from Mycobacterium tuberculosis, refined to 1.5 [⁰]A resolution, gives new information concerning the mycolyltransferase mechanism and the interaction of antigen 85 with human fibronectin. The apo structures of 85C reveals an α/β hydrolase fold centered on the catalytic triad formed by Serine 124, Glutamate 228, and Histidine 260. This implies a catalytic mechanism that includes the formation of a negatively charged tetrahedral transition state and subsequent acyl-enzyme intermediate. Additionally, surface residues conserved between the three antigen 85 homologs indicate that it is primarily the N-terminal residues that are responsible for the interaction with human fibronectin. The structure of antigen 85C complexed with the covalent inhibitor, diethyl phosphate, refined to 1.83 []A resolution confirms the proposed mechanism and implicates residues Leucine 40 and Methionine 125 in the formation of an oxyanion hole to stabilize the tetrahedral transition state. A hydrophobic pocket and tunnel extending 21 []A into the core of the protein, indicates the location of a binding site for the mycolate moiety of the substrate. A 2.0 []A co-crystal structure of Antigen 85C with Octyl thioglucocide (OSG) confirms the proposed binding mode of substrate within the active site, and gives new information concerning important interactions necessary for substrate binding, specifically binding of the carbohydrate moiety. Additionally, the crystal structure of antigen 85A was refined to 2.7[]A resolution. This confirmed the structural conservation of N-terminal residues proposed to interact with human fibronectin, and the structural conservation of the residues forming the active site. The proposed catalytic mechanism and information concerning substrate/enzyme interactions has allowed for preliminary design of carbohydrate based anti-tubercular compounds. |
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| Item Description: | Vita. "Major Subject: Biochemistry". In title numerals are used. |
| Physical Description: | xiv, 231 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilm Inc. |
| Bibliography: | Includes bibliographical references (leaves 209-230). |