FIGURE 5.

HA binding domains (HABD) of TSG-6 [(A) PDB code 1O7B; (B) PDB code 2PF5] and CD44 [(C) PDB code 1POZ; (D) PDB code 1UUH]. In the models, the TSG-6 or CD44 residues participate in binging are shown in red. The HABD of TSG-6 was the only Link module. The link module was structured by two β-sheets and two α-helices. The two β-sheets were composed of four and two β-strands. CD44 extended the β-sheet at the C- and N-termini on the basis of TSG6 (adding four β strands), and the HABD of CD44 was redefined. Unlike the NMR model (C), due to the low charge density caused by the conformational balance, the crystal (D) does not have a secondary structure in residues 62-73.