As always with our Mycobacterial work, all cryo-EM maps and atomic models are scheduled for immediate release by the wwPDB (@rcsbpdb.bsky.social @pdbeurope.bsky.social etc)

Oops, the picture of mycolic acids (from en.wikipedia.org/wiki/Mycolic...) in the previous skeet isn't displaying properly. Here it is again.

Thanks! Yes, lots of great work has been done on related complexes!
The mycobacterial LCC is pretty weird compared to the others, though: it has one type of subunit (AccD5) for acetyl/propionyl-CoA and another (AccD4) for very long chain acyl-CoA, used to form the alpha branch of mycolic acid:

Interestingly, Yingke found some complexes bound to uncharacterized proteins MSMEG_0435 & 0436 (Rv0263c & 0264c in M. tuberculosis). A recent preprint from Carl Nathan shows that Rv0263c is needed for Mtb survival during transmission, suggesting it modulates mycolic acid synthesis in TB transmission

A structure with short- and long-chain acyl-CoAs shows how the two types of carboxyltransferase (CT) subunit distinguish acyl-CoAs: the short-chain CT subunit binds CoA but can’t accommodate a long acyl chain; the long-chain CT subunit binds long acyl chains but doesn’t interact strongly with CoA.

Adding short-chain acyl-CoA substrate (plus ATP & bicarbonate) causes biotin carboxyl carrier protein (BCCP) domains to travel between biotin carboxylase (BC) domains, which load a carboxyl group onto the BCCP biotin, and the carboxyltransferase (CT) domain, which transfers it to the acyl-CoA.

The MCC complex is well studied, but the long-chain carboxylase (LCC) complex isn’t, and is essential for making mycolic acid for the mycobacterial cell wall. The LCC complex carboxylates both long-chain and short-chain acyl-CoA. A structure with propionyl-CoA shows how it binds short-chain acyl-CoA