Isolation, Characterization, and Molecular Modeling of a Rheumatoid Factor from a Hepatitis C Virus Infected Patient with Sjögren's Syndrome

Lee, Yu-Ching; Tsai, Keng-Chang; Leu, Sy-Jye; Wang, Tuan-Jen; Liu, Chia-Yu; Yang, Yi-Yuan

The CDR-H3 loop forms a finger-like structure extending into the bottom of a deep pocket of the IgG Fc, which is composed of Arg355, Ser442, Pro352(L), and Pro352(H). Four different interactions are generated by the H3 loop and Fc, namely, ion interaction, cation-pi interactions, Hbonding, and hydrophobic interactions. The IgG Fc-binding surface contains a main charged residue Arg355 which is involved in the ion interaction to Asp104 and the cationpi interactions to Tyr106 and Tyr107 on the CDR-H3 loop ( Figure 8) . Moreover, the side chain of Phe105 on the CDR-H3 loop interacts with Pro352 in the H/L chain of C 3 domains via two hydrophobic contacts. The Thr102 side chain and Thr103 side chain on the CDR-H3 loop, respectively, interact with Ser444 and Ser442 on the IgG Fc, both resulting in the formation of H-bonding.