MmlI is a short, approx 115 residue, protein of two alpha helices and four beta strands. It is involved in the catabolism of methyl-substituted aromatics via a modified oxo-adipate pathway in bacteria. The enzyme appears to be monomeric in some species [1] and tetrameric in others [2]. The known structure shows two copies of the protein form a dimeric alpha beta barrel.

1: Purification and characterization of 4-methylmuconolactone methylisomerase, a novel enzyme of the modified 3-oxoadipate pathway in the gram-negative bacterium Alcaligenes eutrophus JMP 134. Pieper DH, Stadler-Fritzsche K, Knackmuss HJ, Engesser KH, Bruce NC, Cain RB; Biochem J. 1990;271:529-534. PMID:2241929

2: Purification and characterization of 4-methylmuconolactone methyl-isomerase, a novel enzyme of the modified 3-oxoadipate pathway in nocardioform actinomycetes. Bruce NC, Cain RB, Pieper DH, Engesser KH; Biochem J. 1989;262:303-312. PMID:2818569