| Description: |
The ubiquitous 2-oxoacid dehydrogenases are a family of very large multienzymecomplexes consisting of multiple copies of at least three enzymes whichcatalyze the oxidative decarboxylation of several different 2-oxoacids,resulting in acyl-CoA products. Members of this family include pyruvatedehydrogenase (PDH), 2-oxoglutarate dehydrogenase (OGDH) and branched-chain 2-oxoacid dehydrogenase (BCDH). The three enzymes assembling to form thesecomplexes are the decarboxylase E1 (called E1p, E1o and E1b in PDH, OGDH andBCDH, respectively), dihydrolipoamide acetyl, succinyl and branched-chaintransferase E2 (E2p, E2o and E2b, respectively) and dihydrolipoamidedehydrogenase E3. The E3 component is identical in all three complexes (PDH,OGDH and BCDH) and catalyzes the same reaction. The structural core of all 2-oxoacid dehydrogenase complexes (ODHc) is formed of multiple copies of E2subunits, with the E1 and E3 subunits bound on the periphery. The E2 componentof the ODHc's of both bacteria and eukaryotes serves as the structural core ofthese multienzyme complexes and is comprised of three types of domains.Starting with the N terminus, there are 1-3 tandem repeated lipoyl domains(LD), followed by a peripheral subunit-binding domain (PSBD)responsible for binding E1/E3 chains. The third domain is the C-terminalcatalytic domain (CD). The individual domains are separated by long, flexiblelinker regions allowing large movements of the lipoyl domain(s) to enableactive site coupling. The PSBD domain binds E1 or E3, but not bothsimultaneously. The flexible linker allows the PSBD domain (associated witheither E1 or E3) to move quite freely with respect to the core formed E2catalytic domains [, , , , ].The ~35-residue PSBD domain has a compact structure consisting of two short,parallel α-helices (H1 and H2) separated by a loop (L1), a single helicalturn, and a further, less well-ordered loop (L2) (see PDB:1BAL). The compactstructure of the PSBD domain is stabilized mainly by hydrophobic interactions.The interactions between the PSBD domain and E3 are all mediated by chargedside chains, forming an 'electrostatic zipper'. The residues of the PSBDdomain involved in the interactions are all provided by helix H1 of thisdomain. Helix H2 of PSBD does not interact with E3, but may be involved inbinding E1 [, , ]. |
