Required for methylation of hopanoids at the C-3 position. Binds 1 [4Fe-4S] cluster. The cluster is coordinated with 3 cysteines and an exchangeable S-adenosyl-L-methionine. Deletion mutant can produce both the desmethyl aminobacteriohopanepentol and aminobacteriohopanetetrol but not their C-3 methylated counterparts. Deletion results in reduced intracytoplasmic membranes and in decreased survival in late stationary phase. Belongs to the radical SAM superfamily.