Fig. 4. Molecular modeling of light chains.

(A) S35 and S38 light chains. In the case of S38, the amino acid residues of Asp¹, Ser27a, and His27d (or His⁹³) are considered to form a catalytic triad-like structure, although the distances are slightly long. The distance between Ser27a(O) and His27d (N) is 10.37 Å in S35 and 10.43 Å in S38. The distance between His27d(N) and Asp1(O) is 17.42 Å in S35 and 13.77 Å in S38. The S38 distance is shorter than the S35 distance by 3.65 Å, suggesting that Asp¹ can approach His27d. (B) T99wt and T99-Pro95(−) light chains. In this case, a catalytic triad composed of Asp¹, Ser27a, and His⁹³ is preferable. The distance between Ser27a(O) and His93(N) is 7.66 Å in T99wt and 6.20 Å in T99-Pro95(−). The distance between His93(N) and Asp1(O) changed from 12.26 Å in T99wt to 6.208 Å in T99-Pro95(−), and the residues face each other. This is a crucial change from which the catalytic triad can be derived.