Position of mutated residues. Mutated residues are shown in the structure of Irga6-M173A . The protein backbone is shown as follows: the N-terminal helical domain (cyan), the G-domain (light-blue), the linker-helix (gray) and the C-terminal helical domain (dark blue). The surface formed by the following residues is shown: (i) Glu77, Thr102, Gly103, Glu106, Thr108, Ser132, Arg159, Lys161, Asp164, Asn191 and Lys196 define the catalytic interface (red); (ii) Lys162 is located at the border of the catalytic interface and the secondary patch (orange); (iii) Arg31, Lys32, Lys169, Lys176, Arg210 and Lys246 define the secondary patch (yellow); (iv) Ser18, Glu37, Glu43, Leu44, Lys48, Asn50, Gln52, Ser56, Glu64, Thr88, Glu97, Lys101, Met109, Glu110, Arg111, Lys115, Glu142, Lys145, Glu148, Asp150, Ser172, Ala173 (instead of Met173), Lys175, Glu177, Lys202, Glu203, Arg218, Glu219, Glu224, His237, Val242, Asp245, Asp250, Lys255, Asn265, Ser269, Arg275, Glu285, Asn293, Ser304, Lys310, Lys311, Thr325, Ser326, Glu335, Lys346, Asp355, Glu356, Glu357, Leu372, Ala373 and Lys407 did not prevent oligomerisation, when mutated (green). Lys9 and Ser10 are not resolved in the crystal structure. (a) Front view of the G-domain. (b) Rear view; Figure 1a rotated by 180° around y-axis. (c) Top view; Figure 1a rotated by 90° around x-axis. (d) Bottom view; Figure 1c rotated by 180° around y-axis. (e) Right view; Figure 1a rotated by 90° around y-axis. (f) Left view; Figure 1e rotated by 180° around y-axis.