title: Cysteine protease attribute of eukaryotic ribosomal protein S4.
abstract: BACKGROUND
  Ribosomal proteins often carry out extraribosomal functions. The protein S4 from the smaller subunit of Escherichia coli, for instance, regulates self synthesis and acts as a transcription factor. In humans, S4 might be involved in Turner syndrome. Recent studies also associate many ribosomal proteins with malignancy, and cell death and survival. The list of extraribosomal functions of ribosomal proteins thus continues to grow.
  
  
  METHODS
  Enzymatic action of recombinant wheat S4 on fluorogenic peptide substrates Ac-XEXD↓-AFC (N-acetyl-residue-Glu-residue-Asp-7-amino-4-trifluoromethylcoumarin) and Z-FR↓-AMC (N-CBZ-Phe-Arg-aminomethylcoumarin) as well as proteins has been examined under a variety of solution conditions.
  
  
  RESULTS
  Eukaryotic ribosomal protein S4 is an endoprotease exhibiting all characteristics of cysteine proteases. The K(m) value for the cleavage of Z-FR↓-AMC by a cysteine mutant (C41F) is about 70-fold higher relative to that for the wild-type protein under identical conditions, implying that S4 is indeed a cysteine protease. Interestingly, activity responses of the S4 protein and caspases toward environmental parameters, including pH, temperature, ionic strength, and Mg(2+) and Zn(2+) concentrations, are quite similar. Respective kinetic constants for their cleavage action on Ac-LEHD↓-AFC are also similar. However, S4 cannot be a caspase, because unlike the latter it also hydrolyzes the cathepsin substrate Z-FR↓-AMC.
  
  
  CONCLUSIONS
  The eukaryotic S4 is a generic cysteine protease capable of hydrolyzing a broad spectrum of synthetic substrates and proteins. The enzyme attribute of eukaryotic ribosomal protein S4 is a new phenomenon. Its possible involvement in cell growth and proliferations are presented in the light of known extraribosomal roles of ribosomal proteins.
authors.affiliation: School of Chemistry, University of Hyderabad, Hyderabad 500 046, India.
authors.forename: Babu
authors.initials: B
authors.lastname: Sudhamalla
authors.forename: Madasu
authors.initials: M
authors.lastname: Yadaiah
authors.forename: Dasari
authors.initials: D
authors.lastname: Ramakrishna
authors.forename: Abani K
authors.initials: AK
authors.lastname: Bhuyan
mesh_terms: D000818:Animals; D057056:Cysteine Proteases / Q000737:chemistry / Q000378:metabolism / Q000502:physiology; D004789:Enzyme Activation / Q000187:drug effects; D056890:Eukaryota / Q000201:enzymology / Q000378:metabolism; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D006801:Humans; D008274:Magnesium / Q000494:pharmacology; D051379:Mice; D008958:Models, Molecular; D009994:Osmolar Concentration; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism; D017510:Protein Folding; D059748:Proteolysis / Q000187:drug effects; D012269:Ribosomal Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D013696:Temperature; D013822:Thermoplasma / Q000737:chemistry / Q000201:enzymology / Q000378:metabolism; D014908:Triticum / Q000737:chemistry / Q000201:enzymology / Q000378:metabolism; D051020:bcl-X Protein / Q000378:metabolism
chemical_list: C494812:Bcl2l1 protein, mouse; D015852:Eukaryotic Initiation Factor-2; D010940:Plant Proteins; D012269:Ribosomal Proteins; D051020:bcl-X Protein; C031798:ribosomal protein S4; D057056:Cysteine Proteases; D008274:Magnesium