| Type: | Family | Name: | Hopanoid biosynthesis associated radical SAM protein HpnH |
| Description: | Proteins in this entry are members of the radical SAM superfamily of enzymes that utilise an iron-sulphur redox cluster and S-adenosylmethionine to carry out diverse radical mediated reactions []. This group of proteins are frequently encoded in the same locus as squalene-hopene cyclase (SHC, ) and other proteins associated with the biosynthesis of hopanoid natural products. The linkage between SHC and this radical SAM enzyme is strong; one is nearly always observed in the same genome where the other is found. A hopanoid biosynthesis locus was described in Zymomonas mobilisconsisting of the genes for HpnA-E and SHC (HpnF) []. Continuing past SHC are the genes for a phosphorylase enzyme (ZMO0873, i.e. HpnG, ) and this radical SAM enzyme (ZMO0874) which we name here HpnH. Granted, in Z. mobilis, HpnH is in a convergent orientation with respect to HpnA-G, but one gene beyond HpnH and running in the same convergent direction is IspH (ZM0875, 4-hydroxy-3-methylbut-2-enyl diphosphate reductase), an essential enzyme of IPP biosynthesis and therefore essential for the biosynthesis of hopanoids. One of the well-described hopanoid intermediates is bacteriohopanetetrol. In the conversion from hopene several reactions must occur in the side chain for which a radical mechanism might be reasonable. These include the four (presumably anaerobic) hydroxylations and a methyl shift. | Short Name: | Hopanoid_synth-assoc_rSAM_HpnH |
