PDBsum entry 1iu4

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Transferase PDB id
Protein chains
331 a.a.
Waters ×550

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Title Crystal structure of microbial transglutaminase from streptoverticillium mobaraense.
Authors T.Kashiwagi, K.Yokoyama, K.Ishikawa, K.Ono, D.Ejima, H.Matsui, E.Suzuki.
Ref. J Biol Chem, 2002, 277, 44252-44260. [DOI no: 10.1074/jbc.M203933200]
PubMed id 12221081
The crystal structure of a microbial transglutaminase from Streptoverticillium mobaraense has been determined at 2.4 A resolution. The protein folds into a plate-like shape, and has one deep cleft at the edge of the molecule. Its overall structure is completely different from that of the factor XIII-like transglutaminase, which possesses a cysteine protease-like catalytic triad. The catalytic residue, Cys(64), exists at the bottom of the cleft. Asp(255) resides at the position nearest to Cys(64) and is also adjacent to His(274). Interestingly, Cys(64), Asp(255), and His(274) superimpose well on the catalytic triad "Cys-His-Asp" of the factor XIII-like transglutaminase, in this order. The secondary structure frameworks around these residues are also similar to each other. These results imply that both transglutaminases are related by convergent evolution; however, the microbial transglutaminase has developed a novel catalytic mechanism specialized for the cross-linking reaction. The structure accounts well for the catalytic mechanism, in which Asp(255) is considered to be enzymatically essential, as well as for the causes of the higher reaction rate, the broader substrate specificity, and the lower deamidation activity of this enzyme.
Figure 5.
Fig. 5. Structural comparison of MTG and FTG. A, overall structures; B, structures around the active sites of MTG (left) and FTG (right). The top views of MTG are drawn with a green ribbon model. The four domains of FTG ( -sandwich, core, barrel 1, and barrel 2) are shown in light blue, dark blue, light purple, and dark purple, respectively. The catalytic triad of FTG (Cys272, His332, and Asp355) and the positionally corresponding residues of MTG (Cys64, Asp255, and His274) are represented by the red wire model. These illustrations were drawn using the program QUANTA (Molecular Simulation Inc.). In A, the regions enclosed by yellow circles, a green circle, and a purple circle represent active sites, a possible acyl donor binding site of FTG, and a possible acyl acceptor binding site of FTG, respectively. C, stereo view of the superposition of the active site of MTG (green) on those of FTG (light blue). The catalytic triads of FTG and MTG, as well as the residues (S293(MTG) and Y515(FTG)) in which the side chains interact with the side chains of the catalytic triads (H274(MTG) and C272(FTG), respectively), are represented. The ball-and-stick representations were drawn using the program MOLSCRIPT.
Figure 6.
Fig. 6. A hypothetical catalytic mechanism of MTG. Gln and Lys are the residues of substrate proteins. Although it has been shown that His 274 is not essential for the catalytic activity (see footnote 3), we have included His274 in this figure for comparison with the catalytic mechanism of factor XIII, etc. Although the candidates for the oxyanion hole-constructing residues are mentioned in the text, for clarity, they were omitted from this figure.
The above figures are reprinted by permission from the ASBMB: J Biol Chem (2002, 277, 44252-44260) copyright 2002.
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