Last modified 6th April '95 © Birkbeck College 1995

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A Rough Guide to Protein Types

This is meant to provide a quick and dirty overview, and is not exhaustive, although it is hoped that it helps in appreciating the wide variety of roles that various different forms of protein fulfill. You will appreciate the links on this resource best if you have RasMol installed, and configured for Chemical MIME.
Firstly three classes that are a little separate from the bulk of proteins :-

1.Integral Membrane Proteins

eg photosynthetic reaction centre, bacteriorhodopsin, 7-trans-membrane helix G-protein-coupled receptors, nicotinic acetylcholine receptor, various proton and ion pumps, voltage-gated ion channels, gap junction proteins, etc.

2.Fibrous and Structural Proteins

3.Viral Proteins

Coat proteins, integrases, proteases, RNaseH/Reverse Transcriptase



Hundreds or thousands of them - catalysing all the biochemical pathways, mostly in the cytosol - transferases, hydrolases, lyases, isomerases, etc.
Many are variations on the basic Rossman-fold (as in lactate dehydrogenase) Many use ATP and/or other co-factors, such as metal ions, mono- or dinucleotides, flavins, etc.
Often multimers, with allosteric cooperativity

Nucleic Acid Manipulation and Regulation Proteins

Polymerases, nucleases, ligases, gyrases, topo-isomerases, DNA-binding proteins, transcription factors, zinc-fingers, repressors, histones, steroid receptors

Response Elements

Elements of 2nd.messenger pathways - kinases, phosphatases, G-proteins, calmodulin, lipases, adaptors ( SH2, SH3, PH domains), etc.
Calcium ions and phosphate groups play a large role here.
Some of these are membrane associated.

Redox and Electron Transport Proteins

e.g. dismutases, cytochromes, thioredoxin, ferredoxin, etc.
Haem groups and metal ions often employed as co-factors



Nucleases cut nucleic acids (eg pancreatic RNase) and
Lipases cut and process lipid chains, and
Glycosidases cut sugar moieties, (eg lysozyme, and
Proteinases `cut' other peptide chains - there are FOUR main classes