Cysteine protease attribute of eukaryotic ribosomal protein S4

• Published in: Biochimica et biophysica acta 2012-10, Vol.1820 (10), p.1535-1542
• Main Authors: Sudhamalla, Babu, Yadaiah, Madasu, Ramakrishna, Dasari, Bhuyan, Abani K.
• Format: Article
• Language: English
• Subjects: Animals; bcl-X Protein - metabolism; Caspase substrate cleavage; caspases; cathepsins; cell death; cell growth; cysteine; Cysteine Proteases - chemistry; Cysteine Proteases - metabolism; Cysteine Proteases - physiology; Enzyme Activation - drug effects; Escherichia coli; Eukaryota - enzymology; Eukaryota - metabolism; Eukaryotic Initiation Factor-2 - metabolism; Humans; ionic strength; magnesium; Magnesium - pharmacology; Mice; Models, Molecular; mutants; Non-caspase cysteine protease; Osmolar Concentration; Plant Proteins - chemistry; Plant Proteins - metabolism; Protein Folding; Proteolysis - drug effects; Ribosomal protein S4; ribosomal proteins; Ribosomal Proteins - chemistry; Ribosomal Proteins - metabolism; Ribosomal Proteins - physiology; Specificity of caspase substrates; Temperature; Thermoplasma - chemistry; Thermoplasma - enzymology; Thermoplasma - metabolism; transcription factors; Triticum - chemistry; Triticum - enzymology; Triticum - metabolism; wheat; zinc
• ISSN: 0304-4165; 0006-3002; 1872-8006
• DOI: 10.1016/j.bbagen.2012.05.001

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. 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. Eukaryotic ribosomal protein S4 is an endoprotease exhibiting all characteristics of cysteine proteases. The Km 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 Mg2+ and Zn2+ 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. 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. ► The eukaryotic ribosomal protein S4 is a cysteine protease. ► It cleaves synthetic substrates commonly used for assaying cathepsins and caspases. ► Proteolysis of at least two recombinant proteins, Bcl-xL and eIF2α, is demonstrated. ► The extraribsosomal activity of S4 could have roles in cell growth and proliferation.