Tham khảo tài liệu 'protein purification part 8', khoa học tự nhiên, công nghệ sinh học phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 98 Protein Purification 1 10 20 30 40 45 z ALB8-CA LKNAKgDAIA ELKKAGiTSD FYFNAINKAK TVEgVNALKN EILKA ABD3 LAEAKV0ANR ELDKYGV SD YYKNLINNAK TVEGVKALin EILAA ABDI LAKAKAgAgK EFNKYGV SD YYKNLINNAK TVEGVKgLQA QVVES ABD2 la eakvBanr ELDKYGV SD YÌKNLINNAK TVEGVK LQA QVVES Fig. 6. Sequence alignment of the albumin-binding domains of SPA together with the second GA-module derived from F. magna ALB8-GA . Differences are highlighted and only the 4445 amino acid motifs that are most highly conserved are displayed. The structure of the domain is also shown Reconstructed from PDB structure 1GJT Johansson et al. 2002a . Fig. 7. Overview of binding sites of IgG-binding domain C2 from SPG to A Fab and B Fc. The binding of the GA-module of PAB to HSA is shown in C Reconstructed from PDB structures 1QKZ 1FCC and 1TF0 . them Sauer-Eriksson et al. 1995 . SPG-domains bind to the cleft between CH2 and CH3 figure 7A as opposed to the domains of SPA which bind more on the CH2 side of Fc. However in the complex the third strand of the SPG-domain is situated approximately in the same region as the first Fc-binding helix of the SPA-domain. Consequently SPA and SPG cannot simultaneously bind the same Fc-molecule Stone et al. 1989 . Furthermore the interactions between SPG and Fc involve many charged and polar residues forming hydrogen bonds and salt bridges while the binding between SPA and Fc involve mostly hydrophobic interactions Sauer-Eriksson et al. 1995 . The strength of the binding to Fc has been determined using SPR to around 20-100 nM for the C2-domain and low nanomolar values for the whole SPG molecule have been reported Akerstrom Bjorck 1986 Gulich et al. 2002 Sagawa et al. 2005 . The binding of SPA and SPG to Fc is pH-dependent. SPG binds most efficiently to IgG at pH 4-5 and the binding is weakened with increased pH. SPA on the other hand binds with highest affinity at pH 8 Akerstrom Bjorck 1986 . This difference is due to the composition of the interaction interfaces. C3 has .
