MIF proteins are theta‐class glutathione S‐transferase homologs

Abstract

MIF proteins are mammalian polypeptides of approximately 13,000 molecular weight. This class includes human macrophage migration inhibitory factor (MIF), a rat liver protein that has glutathione S-transferase (GST) activity (TRANSMIF), and the mouse delayed early response gene 6 (DER6) protein. MIF proteins were previously linked to GSTs by demonstrating transferase activity and observing N-terminal sequence homology with a mu-class GST (Blocki, EA., Schlievert, P.M., & Wackett, L.P., 1992, Nature360, 269-270). In this study, MIF proteins are shown to be structurally related to the theta class of GSTs. This is established in three ways. First, unique primary sequence patterns are developed for each of the GST gene classes. The patterns identify the three MIF proteins as theta-like transferase homologs. Second, pattern analysis indicates that GST members of the theta class contain a serine residue in place of the N-terminal tyrosine that is implicated in glutathione deprotonation and activation in GSTs of known structure (Liu, S., et al., 1992, J. Biol. Chem. 267, 4296-4299). The MIF proteins contain a threonine at this position. Third, polyclonal antibodies raised against recombinant human MIF crossreact on Western blots with rat theta GST but not with alpha and mu GSTs. That MIF proteins have glutathionebinding ability may provide a common structural key toward understanding the varied functions of this widely distributed emerging gene family. Because theta is thought to be the most ancient evolutionary GST class, MIF proteins may have diverged early in evolution but retained a glutathione-binding domain.

Crystal structure at 2.6-A resolution of human macrophage migration inhibitory factor.

“…This showed that: (i) MIF shares 25-35% sequence identity within the first 30 amino acids of GSTs; (ii) a hydroxyl-containing active site residue of GSTs (serine for 0-class GST and tyrosine for a-, ir-, and ,u-class GSTs) is replaced by a threonine at the equivalent position of MIF; and (iii) polyclonal antibodies raised to a liver MIF preparation cross-react with 0-class GST (9,34). Nevertheless, the hypothesis that MIF is related to GST is controversial and has been challenged by the lack of significant sequence homology along the entire polypeptide of MIF, the large difference in size between MIF (13 kDa) and GST (26 kDa) (35), and the absence of GST activity in purified and otherwise biologically active recombinant MIF (21,36).…”

Structure and organization of the human Theta-class glutathione S-transferase and d-dopachrome tautomerase gene complex

“…Since MIF has been shown to have DDCT activity, it is likely that DDCT may have a similar physiological role to that of MIF [41]. Interestingly, MIF was previously suggested to show sequence similarities to Mu-and Theta-class GSTs, and was reported to have GST activity [42,43]. Although an evolutionary relationship between MIF and the GSTs has been disputed [44], the occurrence of a closely related gene (DDCT) within the Theta-class gene cluster is, if nothing else, an interesting coincidence.…”

Protein Engineering Studies of Dichloromethane Dehalogenase/Glutathione S‐Transferase from Methylophilus Sp. Strain DM11

“…Several X-ray structures for GST enzymes of the a, p and ~t classes have become available over the last five years (for reviews, see Dirr et al, 1994 andParker, 1994), followed by structures of GST enzymes from squid (Ji et al,l995), Schistosoma japonicum (Lim et al, 1994;McTigue et al, 1995), by the first X-ray structure of a 8-class GST from the fly Lucilia cuprina , and, most recently, by that of a herbicide-conjugating plant GST from Arubidopsis thaliana (Reinemer et al, 1996), which from its protein sequence falls in the proposed 4 class of GST enzymes (Blocki et al, 1993). As a consequence, the amassed data on substrate specificity and catalytic activity of glutathione S-transferases and mutants thereof, obtained by protein engineering, can now often be discussed in great structural detail.…”

“…Furthermore, two 0-class GST sequences from human and fish have no N-terminal tyrosine residue whatsoever. A search for conserved residues in &class GSTs suggested a well-conserved serine residue at the N-terminal as a potential H-bonding residue in theses enzymes (Blocki et al, 1993). We investigated by protein engineering methods the importance of residues Tyr6, His8 and Serl2 in DMll dichloromethane dehalogenase (Fig.…”