>TIGR02087 LEUD_arch 3-isopropylmalate dehydratase, small subunit; InterPro: IPR011827 3-isopropylmalate dehydratase (or isopropylmalate isomerase; 4.2.1.33 from EC) catalyses the stereo-specific isomerisation of 2-isopropylmalate and 3-isopropylmalate, via the formation of 2-isopropylmaleate. This enzyme performs the second step in the biosynthesis of leucine, and is present in most prokaryotes and many fungal species. The prokaryotic enzyme is a heterodimer composed of a large (LeuC) and small (LeuD) subunit, while the fungal form is a monomeric enzyme. Both forms of isopropylmalate are related and are part of the larger aconitase family . Aconitases are mostly monomeric proteins which share four domains in common and contain a single, labile [4Fe-4S] cluster. Three structural domains (1, 2 and 3) are tightly packed around the iron-sulphur cluster, while a fourth domain (4) forms a deep active-site cleft. The prokaryotic enzyme is encoded by two adjacent genes, leuC and leuD, corresponding to aconitase domains 1-3 and 4 respectively , . LeuC does not bind an iron-sulphur cluster. It is thought that some prokaryotic isopropylamalate dehydrogenases can also function as homoaconitase 4.2.1.36 from EC, converting cis-homoaconitate to homoisocitric acid in lysine biosynthesis . Homoaconitase has been identified in higher fungi (mitochondria) and several archaea and one thermophilic species of bacteria, Thermus thermophilus . This entry is most closely related to the 3-isopropylmalate dehydratase IPR004431 from INTERPRO. It also includes members, which cluster with other genes of leucine biosynthesis. The structure of the Pyrococcus horikoshii small subunit (O59393 from SWISSPROT) has recently been determined . As expected the structure of this polypeptide is similar to that of aconitase domain 4, though one alpha helix is replaced by a short loop with relatively high temperature factor values. This loop region is thought to be important for substrate recognition. Unlike other aconitase family proteins, this subunit formed a tetramer through disulphide linkages, though it is not expected to interfere with its interaction with the large subunit. These disulphide linkages would be expected to confer thermostability on the enzyme, reflecting the thermophilic lifestyle of the organism.; GO: 0003861 3-isopropylmalate dehydratase activity, 0009098 leucine biosynthetic process, 0009316 3-isopropylmalate dehydratase complex.

Probab=99.92 E-value=4.4e-25 Score=202.32 Aligned_cols=154 Identities=27% Similarity=0.372 Sum_probs=109.6 Q ss_pred EEECCCCCHHHCCCCCCCCCCCCHHHHHHHCCCC-HHHHHHHHHHCCCHHHHHHHHHCCCHHHHHHCCCCCCCCCCEEEC Q ss_conf 9965885723316456555447378889874988-656314565302357776652036012232125777657722453 Q gi|254780451|r 670 CLLGDKITTDHISPAGSIPLQSAAASYLRQRGVK-EKDFNQFGTRRGNHEVMMRGTFSNIRICNYMLGEEGKKGGYTIHY 748 (896) Q Consensus 670 ~~lGD~iTTDHISPAG~I~~~spAg~yL~~~Gv~-~~dfNsygsRRgNhevM~RGtFaNirl~N~l~~~~~~egg~T~~~ 748 (896) T Consensus 4 wkFGDdvDTD~IIPG----------rYLR~--~~D~~eLA~h-------------aM~g~~--P----------eF~--- 43 (159) T TIGR02087 4 WKFGDDVDTDVIIPG----------RYLRT--TDDPDELASH-------------AMEGID--P----------EFA--- 43 (159) T ss_pred EECCCCCCCCEECCC----------CCCCC--CCCHHHHHHH-------------CCCCCC--C----------CHH--- T ss_conf 760686467704585----------22575--4777889987-------------055899--6----------313--- Q ss_pred CCCCEEEHHHHHHHHHHCCCCEEEECCCCCCCCCHHHHHHHHHHHCCEEEEEECCHHHHHHHCCCCCEEEEEECC-CCCC Q ss_conf 899787379999989981998899946777867307999886676170899976478988850535523223317-8989 Q gi|254780451|r 749 PSKEELFIYDAAMRYKVDQVPLVVFAGVEYGNGSSRDWAAKGTRLLGVRSVIAESFERIHRSNLIGMGVIPFAFG-KGIS 827 (896) Q Consensus 749 p~~~~~~iydaA~~Y~~~~~plVViAG~~YG~GSSRdwAAkgp~lLGVkAVIA~SFeRIHrsNLv~mGiLPL~F~-~~~~ 827 (896) T Consensus 44 ---------------~kvr~GDviVAGkNFGcGSSREQA~~ALK~aGv~aviA~SFARIFYRNAIN~GLP~i~~~e~vte 108 (159) T TIGR02087 44 ---------------KKVREGDVIVAGKNFGCGSSREQAALALKAAGVAAVIAESFARIFYRNAINIGLPLIEAKEDVTE 108 (159) T ss_pred ---------------HHCCCCCEEEECCCCCCCCCHHHHHHHHHHCCEEEEEEEECCCHHHHHHHHCCCCEEEECCCCEE T ss_conf ---------------40789978871416477887788999997479048985201660103233325202631689650 Q ss_pred HHHHCCCCCEEEEEECHHHCCCCCEEEEEEEECCCCEEEEEEEEEECCHHHHHHHHCCCHHHHHHHH Q ss_conf 8881989743899726322589973899998189967999999873899999999909836898887 Q gi|254780451|r 828 WKNLNIKGDEIINIRKLKTISPRQESTLEIHYSDGTFKCVPIICCIDTLDEINHLKNGGILQAVLRQ 894 (896) Q Consensus 828 ~~~L~l~G~E~~~i~~~~~l~p~~~v~v~i~~~~g~~~~~~~~~r~dt~~E~~~~~~GGiL~yvlr~ 894 (896) T Consensus 109 ~--~~-dGD~-V~vdl~~----g---eir~-~~~~~--~~--~~~~~~df~L~Il~~GGLl~y~kK~ 159 (159) T TIGR02087 109 L--IK-DGDE-VEVDLEK----G---EIRK-VNGKE--VY--KGRPLPDFLLEILEEGGLLEYLKKR 159 (159) T ss_pred E--EC-CCCE-EEEECCC----C---EEEE-ECCCE--EE--ECCCCCCHHHHHHHCCCEEEECCCC T ss_conf 2--13-7887-8997576----6---0888-57950--78--6468985589998718802201259

HHsearch alignment for GI: 254780451 and conserved domain: TIGR02087