Protease Families, Evolution and Mechanism of Action
A proteolytic enzyme releases an amino acid or a peptide from a protein or larger peptide. Proteolysis is one of the final stages of post-translational processing for many proteins, and is unidirectional. It can occur immediately after biosynthesis or som
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Protease Families, Evolution and Mechanism of Action Neil D. Rawlings
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Proteolytic Enzymes
A proteolytic enzyme releases an amino acid or a peptide from a protein or larger peptide. Proteolysis is one of the final stages of post-translational processing for many proteins, and is unidirectional. It can occur immediately after biosynthesis or some time later when the protein has been directed to the place where it is required to function. Very few proteins are resistant to proteolysis, and ultimately nearly all proteins will be broken down to their component amino acids for re-use, either by the organism itself or by a predator or detritivore. Proteolysis is required to remove the initiating methionine from newly synthesized, cytoplasmic proteins; to remove signal peptides from proteins targeted to the cell’s secretory pathway; to remove targeting signals from proteins targeted to specific organelles such as the mitochondrion or chloroplast; to remove propeptides from enzymes, hormones and receptors that are synthesized as precursors, so that these are activated; to release individual proteins and peptides from polyproteins; to release bioactive peptides from protein precursors; to release proteins from the cell surface (“shedding”); to switch off the signals that peptides and proteins initiate by degrading either them or the proteins they bind to; to recycle amino acids by degrading the proteins; to destroy potentially lethal or toxic proteins from parasites and pathogens; to release antigenic peptides from parasites and pathogens; and to obtain amino acids from food proteins. Pathogens and parasites also use proteolytic enzymes to invade their hosts, and to inactivate any host protein that could harm them or interfere with their reproduction. There are also many pathological situations where the degradation of a protein leads to disease, such as tumour invasion, rheumatoid arthritis or Alzheimer’s disease.
N.D. Rawlings (*) The Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridgeshire CB10 1SA, UK e-mail: [email protected] K. Brix and W. Sto¨cker (eds.), Proteases: Structure and Function, DOI 10.1007/978-3-7091-0885-7_1, © Springer-Verlag Wien 2013
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N.D. Rawlings
Table 1.1 Counts of proteolytic enzymes in model organisms
Species Number of proteolytic enzymes Homo sapiens 600 Mus musculus 660 Drosophila melanogaster 477 Caenorhabditis elegans 359 Arabidopsis thaliana 678 Saccharomyces cerevisiae 117 Escherichia coli 405 Bacillus subtilis 190 Thermoplasma volcanium 43 Counts exclude homologues that are known or thought not to be proteolytic enzymes because essential residues have been replaced, pseudogenes and fragments
Almost all organisms require proteolytic enzymes to function. There are some viruses, which do not encode proteolytic enzymes in their genomes, but even these hi-jack host enzymes to do the processing for them. Table 1.1 shows total number of proteolytic enzymes for selected organisms. The number of proteolytic enzymes in a bacterium depends on the sequence
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