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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 ...
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]
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.
Structural Classification of Proteins (SCOP) Protein structure databases CATH database: Protein structure databases ModBase: Sali Lab, UCSF: database of comparative protein structure models Protein model databases SIMAP: database of protein similarities computed using FASTA: Protein model databases Swiss-model: server and repository for protein ...
Numerous protein structures are the result of rational design and do not exist in nature. Proteins can be designed from scratch (de novo design) or by making calculated variations on a known protein structure and its sequence (known as protein redesign). Rational protein design approaches make protein-sequence predictions that will fold to ...
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 ...
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 ]
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 ...