{"metadata":{"accession":"PF07754","entry_id":null,"type":"domain","go_terms":null,"source_database":"pfam","member_databases":null,"integrated":"IPR011668","hierarchy":null,"name":{"name":"Ribosomal protein aS21","short":"Ribosomal_aS21"},"description":[{"text":"<p>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 [[cite:PUB00096940]] and has been identified in ribosome structures from Pyrococcus abyssi [[cite:PUB00114374]] and Pyrobaculum calidifontis [[cite:PUB00161770]], 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 [[cite:PUB00161688]], 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 [[cite:PUB00096940]]. 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 [[cite:PUB00114374]]. The widespread conservation of this protein in archaeal genomes supports its role as a core ribosomal component [[cite:PUB00114374],[cite:PUB00161770]].</p>","llm":false,"checked":false,"updated":false}],"wikipedia":null,"literature":{"PUB00161688":{"PMID":32555463,"ISBN":null,"volume":"583","issue":"7817","year":2020,"title":"Dynamic RNA acetylation revealed by quantitative cross-evolutionary mapping.","URL":null,"raw_pages":"638-643","medline_journal":"Nature","ISO_journal":"Nature","authors":["Sas-Chen A","Thomas JM","Matzov D","Taoka M","Nance KD","Nir R","Bryson KM","Shachar R","Liman GLS","Burkhart BW","Gamage ST","Nobe Y","Briney CA","Levy MJ","Fuchs RT","Robb GB","Hartmann J","Sharma S","Lin Q","Florens L","Washburn MP","Isobe T","Santangelo TJ","Shalev-Benami M","Meier JL","Schwartz S."],"DOI_URL":"https://doi.org/10.1038/s41586-020-2418-2"},"PUB00114374":{"PMID":32029867,"ISBN":null,"volume":"3","issue":"1","year":2020,"title":"Cryo-EM study of an archaeal 30S initiation complex gives insights into evolution of translation initiation.","URL":null,"raw_pages":"58","medline_journal":"Commun Biol","ISO_journal":"Commun Biol","authors":["Coureux PD","Lazennec-Schurdevin C","Bourcier S","Mechulam Y","Schmitt E."],"DOI_URL":null},"PUB00096940":{"PMID":32905660,"ISBN":null,"volume":null,"issue":null,"year":2020,"title":"Biological functions, genetic and biochemical characterization, and NMR structure determination of the small zinc finger protein HVO_2753 from Haloferax volcanii.","URL":null,"raw_pages":null,"medline_journal":"FEBS J","ISO_journal":"FEBS J","authors":["Zahn S","Kubatova N","Pyper DJ","Cassidy L","Saxena K","Tholey A","Schwalbe H","Soppa J."],"DOI_URL":null},"PUB00161770":{"PMID":40676158,"ISBN":null,"volume":"10","issue":"8","year":2025,"title":"Structure of an archaeal ribosome reveals a divergent active site and hibernation factor.","URL":null,"raw_pages":"1940-1953","medline_journal":"Nat Microbiol","ISO_journal":"Nat Microbiol","authors":["Nissley AJ","Shulgina Y","Kivimae RW","Downing BE","Penev PI","Banfield JF","Nayak DD","Cate JHD."],"DOI_URL":"https://doi.org/10.1038/s41564-025-02065-w"}},"set_info":{"accession":"CL0167","name":"Zn_Beta_Ribbon"},"overlaps_with":null,"counters":{"subfamilies":0,"domain_architectures":1,"interactions":0,"matches":557,"pathways":0,"proteins":557,"proteomes":551,"sets":1,"structural_models":{"alphafold":526},"structures":33,"taxa":1013},"entry_annotations":{"hmm":0,"logo":0,"alignment:seed":9,"alignment:full":263},"cross_references":{},"is_llm":false,"is_reviewed_llm":false,"is_updated_llm":false,"representative_structure":null}}