This entry represents ribosomal protein aS21, an archaea-specific component of the small ribosomal subunit (SSU). The protein was first characterised as HVO_2753 (Small CPxCG-related zinc finger protein) from Haloferax volcanii [1] and has been ident ...
This entry represents ribosomal protein aS21, an archaea-specific component of the small ribosomal subunit (SSU). The protein was first characterised as HVO_2753 (Small CPxCG-related zinc finger protein) from Haloferax volcanii [1] and has been identified in ribosome structures from Pyrococcus abyssi [3] and Pyrobaculum calidifontis [4], where it is located at a position corresponding to eS21 in eukaryotic ribosomes. NMR 3D structure analysis revealed four C(P)XCG motifs, suggesting the presence of two zinc-binding pockets (ZBPs). While some members of this entry bind two zinc ions [2], in HVO_2753, only C(P)XCG motifs 2 and 4 (comprising Cys-32 to Cys-35 and Cys-50 to Cys-53) form a ZBP and bind one zinc atom, while C(P)XCG motifs 1 and 3 (comprising Cys-12 to Cys-15 and Cys-39 to Cys-42) form a four-Cys cluster that do not bind zinc. The four C(P)XCG motifs are critical for protein stability, folding and functionality [1]. Despite structural topology resembling eukaryotic eS21, sequence identities in the structurally superimposed regions are limited, and the archaeal protein contains two zinc knuckles not observed in the eukaryotic version [3]. The widespread conservation of this protein in archaeal genomes supports its role as a core ribosomal component [3,4].
