Allosteric Regulation and Communication between Subunits in Uracil Phosphoribosyltransferase from Sulfolobus solfataricus
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- 作者：Susan Arent ; Pernille Harris ; Kaj Frank Jensen ; and Sine Larsen
- 刊名：Biochemistry
- 出版年：2005
- 出版时间：January 25, 2005
- 年：2005
- 卷：44
- 期：3
- 页码：883 - 892
- 全文大小：850K
- 年卷期：v.44,no.3(January 25, 2005)
- ISSN：1520-4995
文摘
Uracil phosphoribosyltransferase (UPRTase) catalyzes the conversion of 5-phosphate-
-1-diphosphate (PRPP) and uracil to uridine 5'-monophosphate (UMP) and diphosphate. The UPRTase fromSulfolobus solfataricus has a unique regulation by nucleoside triphosphates compared to UPRTases fromother organisms. To understand the allosteric regulation, crystal structures were determined for S.solfataricus UPRTase in complex with UMP and with UMP and the allosteric inhibitor CTP. Also, astructure with UMP bound in half of the active sites was determined. All three complexes form tetramersbut reveal differences in the subunits and their relative arrangement. In the UPRTase-UMP complex, thepeptide bond between a conserved arginine residue (Arg80) and the preceding residue (Leu79) adopts acis conformation in half of the subunits and a trans conformation in the other half and the tetramer comprisestwo cis-trans dimers. In contrast, four identical subunits compose the UPRTase-UMP-CTP tetramer.CTP binding affects the conformation of Arg80, and the Arg80 conformation in the UPRTase-UMP-CTP complex leaves no room for binding of the substrate PRPP. The different conformations of Arg80coupled to rearrangements in the quaternary structure imply that this residue plays a major role in regulationof the enzyme and in communication between subunits. The ribose ring of UMP adopts alternativeconformations in the cis and trans subunits of the UPRTase-UMP tetramer with associated differencesin the interactions of the catalytically important Asp209. The active-site differences have been related toproposed kinetic models and provide an explanation for the regulatory significance of the C-terminalGly216.
-1-diphosphate (PRPP) and uracil to uridine 5'-monophosphate (UMP) and diphosphate. The UPRTase fromSulfolobus solfataricus has a unique regulation by nucleoside triphosphates compared to UPRTases fromother organisms. To understand the allosteric regulation, crystal structures were determined for S.solfataricus UPRTase in complex with UMP and with UMP and the allosteric inhibitor CTP. Also, astructure with UMP bound in half of the active sites was determined. All three complexes form tetramersbut reveal differences in the subunits and their relative arrangement. In the UPRTase-UMP complex, thepeptide bond between a conserved arginine residue (Arg80) and the preceding residue (Leu79) adopts acis conformation in half of the subunits and a trans conformation in the other half and the tetramer comprisestwo cis-trans dimers. In contrast, four identical subunits compose the UPRTase-UMP-CTP tetramer.CTP binding affects the conformation of Arg80, and the Arg80 conformation in the UPRTase-UMP-CTP complex leaves no room for binding of the substrate PRPP. The different conformations of Arg80coupled to rearrangements in the quaternary structure imply that this residue plays a major role in regulationof the enzyme and in communication between subunits. The ribose ring of UMP adopts alternativeconformations in the cis and trans subunits of the UPRTase-UMP tetramer with associated differencesin the interactions of the catalytically important Asp209. The active-site differences have been related toproposed kinetic models and provide an explanation for the regulatory significance of the C-terminalGly216.