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From Proteopedia
STRUCTURE OF HUMAN 5'-DEOXY-5'-METHYLTHIOADENOSINE PHOSPHORYLASE AT 1.7 A RESOLUTION
Structural highlights
Disease[MTAP_HUMAN] Defects in MTAP are the cause of diaphyseal medullary stenosis with malignant fibrous histiocytoma (DMSMFH) [MIM:112250]. An autosomal dominant bone dysplasia characterized by pathologic fractures due to abnormal cortical growth and diaphyseal medullary stenosis. The fractures heal poorly, and there is progressive bowing of the lower extremities. Some patients show a limb-girdle myopathy, with muscle weakness and atrophy. Approximately 35% of affected individuals develop an aggressive form of bone sarcoma consistent with malignant fibrous histiocytoma or osteosarcoma. Note=DMSMFH causing mutations found in MTAP exon 9 result in exon skipping and dysregulated alternative splicing of all MTAP isoforms (PubMed:22464254).[1] Note=Loss of MTAP activity may play a role in human cancer. MTAP loss has been reported in a number of cancers, including osteosarcoma, malignant melanoma and gastric cancer.[HAMAP-Rule:MF_03155] Function[MTAP_HUMAN] Catalyzes the reversible phosphorylation of S-methyl-5'-thioadenosine (MTA) to adenine and 5-methylthioribose-1-phosphate. Involved in the breakdown of MTA, a major by-product of polyamine biosynthesis. Responsible for the first step in the methionine salvage pathway after MTA has been generated from S-adenosylmethionine. Has broad substrate specificity with 6-aminopurine nucleosides as preferred substrates.[2] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedBACKGROUND: 5'-Deoxy-5'-methylthioadenosine phosphorylase (MTAP) catalyzes the reversible phosphorolysis of 5'-deoxy-5'-methylthioadenosine (MTA) to adenine and 5-methylthio-D-ribose-1-phosphate. MTA is a by-product of polyamine biosynthesis, which is essential for cell growth and proliferation. This salvage reaction is the principle source of free adenine in human cells. Because of its importance in coupling the purine salvage pathway to polyamine biosynthesis MTAP is a potential chemotherapeutic target. RESULTS: We have determined the crystal structure of MTAP at 1.7 A resolution using multiwavelength anomalous diffraction phasing techniques. MTAP is a trimer comprised of three identical subunits. Each subunit consists of a single alpha/beta domain containing a central eight-stranded mixed beta sheet, a smaller five-stranded mixed beta sheet and six alpha helices. The native structure revealed the presence of an adenine molecule in the purine-binding site. The structure of MTAP with methylthioadenosine and sulfate ion soaked into the active site was also determined using diffraction data to 1.7 A resolution. CONCLUSIONS: The overall quaternary structure and subunit topology of MTAP are similar to mammalian purine nucleoside phosphorylase (PNP). The structures of the MTAP-ligand complexes provide a map of the active site and suggest possible roles for specific residues in substrate binding and catalysis. Residues accounting for the differences in substrate specificity between MTAP and PNP are also identified. Detailed information about the structure and chemical nature of the MTAP active site will aid in the rational design of inhibitors of this potential chemotherapeutic target. The MTAP structure represents the first structure of a mammalian PNP that is specific for 6-aminopurines. The structure of human 5'-deoxy-5'-methylthioadenosine phosphorylase at 1.7 A resolution provides insights into substrate binding and catalysis.,Appleby TC, Erion MD, Ealick SE Structure. 1999 Jun 15;7(6):629-41. PMID:10404592[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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