{"database":"biostudies-literature","file_versions":[],"scores":{"citationCount":0,"reanalysisCount":0,"viewCount":61,"searchCount":0},"additional":{"omics_type":["Unknown"],"volume":["38(5)"],"submitter":["Jang DS"],"pubmed_abstract":["Low-barrier hydrogen bonds (LBHBs) have been proposed to have important influences on the enormous reaction rate increases achieved by many enzymes. Δ(5)-3-ketosteroid isomerase (KSI) catalyzes the allylic isomerization of Δ(5)-3-ketosteroid to its conjugated Δ(4)-isomers at a rate that approaches the diffusion limit. Tyr14, a catalytic residue of KSI, has been hypothesized to form an LBHB with the oxyanion of a dienolate steroid intermediate generated during the catalysis. The unusual chemical shift of a proton at 16.8 ppm in the nuclear magnetic resonance spectrum has been attributed to an LBHB between Tyr14 Oη and C3-O of equilenin, an intermediate analogue, in the active site of D38N KSI. This shift in the spectrum was not observed in Y30F/Y55F/D38N and Y30F/Y55F/Y115F/D38N mutant KSIs when each mutant was complexed with equilenin, suggesting that Tyr14 could not form LBHB with the intermediate analogue in these mutant KSIs. The crystal structure of Y30F/Y55F/Y115F/D38N-equilenin complex revealed that the distance between Tyr14 Oη and C3-O of the bound steroid was within a direct hydrogen bond. The conversion of LBHB to an ordinary hydrogen bond in the mutant KSI reduced the binding affinity for the steroid inhibitors by a factor of 8.1-11. In addition, the absence of LBHB reduced the catalytic activity by only a factor of 1.7-2. These results suggest that the amount of stabilization energy of the reaction intermediate provided by LBHB is small compared with that provided by an ordinary hydrogen bond in KSI."],"journal":["Molecules and cells"],"pagination":["409-15"],"full_dataset_link":["https://www.ebi.ac.uk/biostudies/studies/S-EPMC4443282"],"repository":["biostudies-literature"],"pubmed_title":["Contribution of a low-barrier hydrogen bond to catalysis is not significant in ketosteroid isomerase."],"pmcid":["PMC4443282"],"pubmed_authors":["Shin S","Lee HC","Choi G","Choi KY","Lee HJ","Cha HJ","Hong BH","Jang DS"],"view_count":["61"],"additional_accession":[]},"is_claimable":false,"name":"Contribution of a low-barrier hydrogen bond to catalysis is not significant in ketosteroid isomerase.","description":"Low-barrier hydrogen bonds (LBHBs) have been proposed to have important influences on the enormous reaction rate increases achieved by many enzymes. Δ(5)-3-ketosteroid isomerase (KSI) catalyzes the allylic isomerization of Δ(5)-3-ketosteroid to its conjugated Δ(4)-isomers at a rate that approaches the diffusion limit. Tyr14, a catalytic residue of KSI, has been hypothesized to form an LBHB with the oxyanion of a dienolate steroid intermediate generated during the catalysis. The unusual chemical shift of a proton at 16.8 ppm in the nuclear magnetic resonance spectrum has been attributed to an LBHB between Tyr14 Oη and C3-O of equilenin, an intermediate analogue, in the active site of D38N KSI. This shift in the spectrum was not observed in Y30F/Y55F/D38N and Y30F/Y55F/Y115F/D38N mutant KSIs when each mutant was complexed with equilenin, suggesting that Tyr14 could not form LBHB with the intermediate analogue in these mutant KSIs. The crystal structure of Y30F/Y55F/Y115F/D38N-equilenin complex revealed that the distance between Tyr14 Oη and C3-O of the bound steroid was within a direct hydrogen bond. The conversion of LBHB to an ordinary hydrogen bond in the mutant KSI reduced the binding affinity for the steroid inhibitors by a factor of 8.1-11. In addition, the absence of LBHB reduced the catalytic activity by only a factor of 1.7-2. These results suggest that the amount of stabilization energy of the reaction intermediate provided by LBHB is small compared with that provided by an ordinary hydrogen bond in KSI.","dates":{"release":"2015-01-01T00:00:00Z","publication":"2015 May","modification":"2024-10-18T02:47:24.264Z","creation":"2019-03-26T22:32:55Z"},"accession":"S-EPMC4443282","cross_references":{"pubmed":["25947291"],"doi":["10.14348/molcells.2015.2266"]}}