MF7000131 CaiB (Type III CoA transferase in carnitine metabolism) 1xa3 X-ray 1.85 Homodimer Escherichia coli 15518548 Stenmark P, Gurmu D, Nordlund P Biochemistry 2004 44 43 13996-4003 Carnitine is an important molecule in human metabolism, mainly because of its role in the transport of long-chain fatty acids across the inner mitochondrial membrane. Escherichia coli uses carnitine as a terminal electron acceptor during anaerobic metabolism. Bacteria present in our large intestine break down carnitine that is not absorbed in the small intestine. One part of this catabolic pathway is reversible and can be utilized for bioproduction of large amounts of stereochemically pure L-carnitine, which is used medically for the treatment of a variety of human diseases. Here, we present the crystal structure of the E. coli protein CaiB, which is a member of the recently identified type-III coenzyme A (CoA) transferase family and catalyzes the transfer of the CoA moiety between gamma-butyrobetaine-CoA and carnitine forming carnityl-CoA and gamma-butyrobetaine. This is the first protein from the carnitine metabolic pathway to be structurally characterized. The structure of CaiB reveals a spectacular fold where two monomers are interlaced to form an interlocked dimer. A molecule of the crystallization buffer bis-(2-hydroxyethyl)imino-tris(hydroxymethyl)methane (bis-tris) is bound in a large pocket located primarily in the small domain, and we propose that this pocket constitutes the binding site for both substrate moieties participating in the CaiB transfer reaction. The binding of CoA to CaiB induces a domain movement that closes the active site of the protein. This is the first observation of a domain movement in the type-III CoA transferase family and can play an important role in coupling substrate binding to initiation of the catalytic reaction. GO:0008735 L-carnitine CoA-transferase activity GO:0005737 cytoplasm GO:0042413 carnitine catabolic process 2 1 Homooligomeric enzymes Homodimeric enzymes All chains according to the most probable oligomerization state stored in PDBe were considered. A L-carnitine CoA-transferase Escherichia coli P31572 4 403 98% MDHLPMPKFGPLAGLRVVFSGIEIAGPFAGQMFAEWGAEVIWIENVAWADTIRVQPNYPQLSRRNLHALSLNIFKDEGREAFLKLMETTDIFIEASKGPAFARRGITDEVLWQHNPKLVIAHLSGFGQYGTEEYTNLPAYNTIAQAFSGYLIQNGDVDQPMPAFPYTADYFSGLTATTAALAALHKVRETGKGESIDIAMYEVMLRMGQYFMMDYFNGGEMCPRMSKGKDPYYAGCGLYKCADGYIVMELVGITQIEECFKDIGLAHLLGTPEIPEGTQLIHRIECPYGPLVEEKLDAWLATHTIAEVKERFAELNIACAKVLTVPELESNPQYVARESITQWQTMDGRTCKGPNIMPKFKNNPGQIWRGMPSHGMDTAAILKNIGYSENDIQELVSKGLAKVED 405 secondary structure helix 48 60 secondary structure helix 74 79 secondary structure helix 81 87 secondary structure helix 99 111 secondary structure helix 123 128 secondary structure helix 131 139 secondary structure helix 164 172 secondary structure helix 174 177 secondary structure helix 190 215 secondary structure helix 224 232 secondary structure helix 232 241 secondary structure helix 276 288 secondary structure helix 289 293 secondary structure helix 312 326 secondary structure helix 328 340 secondary structure helix 348 352 secondary structure helix 355 362 secondary structure helix 401 409 secondary structure helix 412 422 secondary structure strand 40 44 secondary structure strand 63 68 secondary structure strand 91 95 secondary structure strand 115 119 secondary structure strand 143 148 secondary structure strand 179 180 secondary structure strand 183 184 secondary structure strand 218 223 secondary structure strand 260 265 secondary structure strand 268 273 secondary structure strand 342 345 secondary structure strand 364 368 secondary structure strand 374 378 secondary structure strand 383 384 secondary structure strand 425 426 pfam PF02515 CoA-transferase family III 12 378 B L-carnitine CoA-transferase Escherichia coli P31572 4 403 98% MDHLPMPKFGPLAGLRVVFSGIEIAGPFAGQMFAEWGAEVIWIENVAWADTIRVQPNYPQLSRRNLHALSLNIFKDEGREAFLKLMETTDIFIEASKGPAFARRGITDEVLWQHNPKLVIAHLSGFGQYGTEEYTNLPAYNTIAQAFSGYLIQNGDVDQPMPAFPYTADYFSGLTATTAALAALHKVRETGKGESIDIAMYEVMLRMGQYFMMDYFNGGEMCPRMSKGKDPYYAGCGLYKCADGYIVMELVGITQIEECFKDIGLAHLLGTPEIPEGTQLIHRIECPYGPLVEEKLDAWLATHTIAEVKERFAELNIACAKVLTVPELESNPQYVARESITQWQTMDGRTCKGPNIMPKFKNNPGQIWRGMPSHGMDTAAILKNIGYSENDIQELVSKGLAKVED 405 secondary structure helix 48 60 secondary structure helix 74 79 secondary structure helix 81 87 secondary structure helix 99 111 secondary structure helix 123 128 secondary structure helix 131 139 secondary structure helix 164 172 secondary structure helix 174 177 secondary structure helix 190 215 secondary structure helix 224 232 secondary structure helix 232 241 secondary structure helix 276 288 secondary structure helix 289 293 secondary structure helix 312 326 secondary structure helix 328 340 secondary structure helix 348 352 secondary structure helix 355 362 secondary structure helix 401 409 secondary structure helix 412 423 secondary structure strand 40 44 secondary structure strand 63 68 secondary structure strand 91 95 secondary structure strand 115 119 secondary structure strand 143 148 secondary structure strand 179 180 secondary structure strand 183 184 secondary structure strand 218 223 secondary structure strand 260 265 secondary structure strand 268 273 secondary structure strand 342 345 secondary structure strand 364 368 secondary structure strand 374 378 secondary structure strand 383 384 secondary structure strand 425 426 pfam PF02515 CoA-transferase family III 12 378 Indirect evidence The full structure participates in mutual synergistic folding. CoA-transferase family III The structure of CaiB reveals a spectacular fold where two monomers are interlaced to form an interlocked dimer with large interface (PMID:15518548). The folding path of CaiB and other proteins of this fold must be quite complex because the dimer cannot be formed by the individually folded monomers, partial unfolding would have to take place to break the CaiB dimer, thus it is most probably very stable (PMID:15518548). A N/A B N/A MF7000131 MF7000132 MF7000133 MF7000134 MF7000135 MF7000871