Borchert, T.V., Abagyan, R.A., Kishan, K.V. R., Zeelen, J.Ph., and Wierenga, R.K. (1993). The crystal structure of an engineered monomeric triosephosphate isomerase, monoTIM: the correct modeling of an eight-residue loop. Structure, 1, 205-213

The triosephosphate isomerase (TIM) fold is found in several different classes of enzymes, most of which are oligomeric. TIM itself always functions as a very tight dimer. It has recently been shown that a monomeric form of TIM (monoTIM) can be constructed by replacing a 15-residue interface loop, loop-3, with an eight-residue fragments; modeling suggests that this should result in a short strain-free turn, resulting in the subsequence helix, helix-A3, having an additional turn at its amino terminus. The crystal structure of monoTIM shows that it retains the characteristic TIM-barrel (beta/alpha)8 fold and that the new loop has a structure very close to that predicted. Two other interface loops, loop-1 ad loop-4, which contain the active site residue Lys13 and His95, respectively show significant changes in structure in monoTIM compared with dimeric wild-type TIM. The observed structural differences between monoTIM and wild-type TIM indicate that the dimeric appearance if TIM determines the location and conformation of two of the four catalytic residues .