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At the top level are all alpha proteins (domains consisting of alpha helices), all beta proteins (domains consisting of beta sheets), and mixed alpha helix/beta sheet proteins. While most proteins adopt a single stable fold, a few proteins can rapidly interconvert between one or more folds. These are referred to as metamorphic proteins. [5]
Protein domains allow protein classification by a combination of sequence, structure and function, and they can be combined in many ways. In an early study of 170,000 proteins, about two-thirds were assigned at least one domain, with larger proteins containing more domains (e.g. proteins larger than 600 amino acids having an average of more ...
Modified amino acids are sometimes observed in proteins; this is usually the result of enzymatic modification after translation (protein synthesis). For example, phosphorylation of serine by kinases and dephosphorylation by phosphatases is an important control mechanism in the cell cycle. Only two amino acids other than the standard twenty are ...
Protein dynamics and conformational changes allow proteins to function as nanoscale biological machines within cells, often in the form of multi-protein complexes. [14] Examples include motor proteins, such as myosin, which is responsible for muscle contraction, kinesin, which moves cargo inside cells away from the nucleus along microtubules ...
The study of proteins, generally under the heading of proteomics, is a vast and complex subject, and much effort has been made to classify and categorize, according to the many specific fields of investigation under which they come.
A protein is a complex, high molecular weight organic compound that consists of amino acids joined by peptide bonds. Organize articles about proteins according to a standard protein ontology . Contents
A protein superfamily is the largest grouping of proteins for which common ancestry can be inferred (see homology). Usually this common ancestry is inferred from structural alignment [ 1 ] and mechanistic similarity, even if no sequence similarity is evident. [ 2 ]
SCOP2 prototype was a beta version of Structural classification of proteins and classification system that aimed to more the evolutionary complexity inherent in protein structure evolution. [12] It is therefore not a simple hierarchy, but a directed acyclic graph network connecting protein superfamilies representing structural and evolutionary ...