TY - JOUR
T1 - Crystal structure of a methyltetrahydrofolate- and corrinoid-dependent methyltransferase
AU - Doukov, Tzanko
AU - Seravalli, Javier
AU - Stezowski, John J.
AU - Ragsdale, Stephen W.
N1 - Funding Information:
We thank Henry Bellamy (DOE facility) for his help during the data collection at beamline 1–5 at SSRL. This beamline is supported by US DOE and by the NIH, Biotechnology Resource Program, Division of Research Resources. We are also indebted to Prof. George Sheldrick for using the Se–Met MeTr data as a (successful) test case for his new program SHELXD and Dr. Eric de la Fortelle for his guidance in using the program SHARP. We thank Rowena Matthews for helpful discussions. Preliminary sequence data was obtained from The Institute for Genomic Research website at http://www.tigr.org . This work was supported by NIH grant GM39451 (SWR) and NSF grant OSR-92552255 (JJS/SWR).
PY - 2000/8/15
Y1 - 2000/8/15
N2 - Background: Methyltetrahydrofolate, corrinoid iron-sulfur protein methyltransferase (MeTr), catalyzes a key step in the Wood-Ljungdahl pathway of carbon dioxide fixation. It transfers the N5-methyl group from methyltetrahydrofolate (CH3-H4folate) to a cob(I)amide center in another protein, the corrinoid iron-sulfur protein. MeTr is a member of a family of proteins that includes methionine Synthase and methanogenic enzymes that activate the methyl group of methyltetra-hydromethano(or -sarcino)pterin. We report the first structure of a protein in this family. Results: We determined the crystal structure of MeTr from Clostridium thermoaceticum at 2.2 Å resolution using multiwavelength anomalous diffraction methods. The overall architecture presents a new functional class of the versatile triose phosphate isomerase (TIM) barrel fold. The MeTr tertiary structure is surprisingly similar to the crystal structures of dihydropteroate synthetases despite sharing less than 200% sequence identity. This homology permitted the methyl-H4folate binding site to be modeled. The model suggests extensive conservation of the pterin ring binding residues in the polar active sites of the methyltransferases and dihydropteroate synthetases. The most significant structural difference between these enzymes is in a loop structure above the active site. It is quite open in MeTr, where it can be modeled as the cobalamin binding site. Conclusions: The MeTr structure consists of a TIM barrel that embeds methyl-H4folate and cobamide. All related methyltransferases are predicted to fold into a similar TIM barrel pattern and have a similar pterin and cobamide binding site. The observed structure is consistent with either a 'front' (N5) or 'back' (C8a) side protonation of CH3-H4folate, a key step that enhances the electrophilic character of the methyl group, activating it for nucleophilic attack by Co(I).
AB - Background: Methyltetrahydrofolate, corrinoid iron-sulfur protein methyltransferase (MeTr), catalyzes a key step in the Wood-Ljungdahl pathway of carbon dioxide fixation. It transfers the N5-methyl group from methyltetrahydrofolate (CH3-H4folate) to a cob(I)amide center in another protein, the corrinoid iron-sulfur protein. MeTr is a member of a family of proteins that includes methionine Synthase and methanogenic enzymes that activate the methyl group of methyltetra-hydromethano(or -sarcino)pterin. We report the first structure of a protein in this family. Results: We determined the crystal structure of MeTr from Clostridium thermoaceticum at 2.2 Å resolution using multiwavelength anomalous diffraction methods. The overall architecture presents a new functional class of the versatile triose phosphate isomerase (TIM) barrel fold. The MeTr tertiary structure is surprisingly similar to the crystal structures of dihydropteroate synthetases despite sharing less than 200% sequence identity. This homology permitted the methyl-H4folate binding site to be modeled. The model suggests extensive conservation of the pterin ring binding residues in the polar active sites of the methyltransferases and dihydropteroate synthetases. The most significant structural difference between these enzymes is in a loop structure above the active site. It is quite open in MeTr, where it can be modeled as the cobalamin binding site. Conclusions: The MeTr structure consists of a TIM barrel that embeds methyl-H4folate and cobamide. All related methyltransferases are predicted to fold into a similar TIM barrel pattern and have a similar pterin and cobamide binding site. The observed structure is consistent with either a 'front' (N5) or 'back' (C8a) side protonation of CH3-H4folate, a key step that enhances the electrophilic character of the methyl group, activating it for nucleophilic attack by Co(I).
KW - Carbon dioxide fixation
KW - Cobalamin
KW - Methyltetrahydrofolate
KW - Methyltransferase
KW - One-carbon metabolism
UR - http://www.scopus.com/inward/record.url?scp=0034662752&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0034662752&partnerID=8YFLogxK
U2 - 10.1016/S0969-2126(00)00172-6
DO - 10.1016/S0969-2126(00)00172-6
M3 - Article
C2 - 10997901
AN - SCOPUS:0034662752
SN - 0969-2126
VL - 8
SP - 817
EP - 830
JO - Structure
JF - Structure
IS - 8
ER -