In an unbranched, chain-like biological molecule, such as a protein or a strand of RNA, a structural motif is a three-dimensional structural element or fold within the chain, which appears also in a variety of other molecules. In the context of proteins, the term is sometimes used interchangeably with "structural domain," although a domain need not be a motif nor, if it contains a motif, need not be made up of only one. A polymer (from Greek: πολυ, polu, many; and μέρος, meros, part) is a substance composed of molecules with large molecular mass composed of repeating structural units, or monomers, connected by covalent chemical bonds. ... 3D (left and center) and 2D (right) representations of the terpenoid molecule atisane. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Ribonucleic acid or RNA is a nucleic acid polymer consisting of nucleotide monomers that plays several important roles in the processes that translate genetic information from deoxyribonucleic acid (DNA) into protein products; RNA acts as a messenger between DNA and the protein synthesis complexes known as ribosomes, forms vital portions... Protein folding is the process by which a protein assumes its characteristic functional shape or tertiary structure, also known as the native state. ... Within a protein, a structural domain (domain) is an element of overall structure that is self-stabilizing and often folds independently of the rest of the protein chain. ...

Structural alignment is a major method for discovering significant structural motifs. Structural alignment of thioredoxins from humans and the fly Drosophila melanogaster. ...

Some motifs exhibit both tertiary and secondary structure, and may be regarded as a configuration of secondary structures. Such a description is the basis for many of the names that structural biologists give to particular kinds, such as the helix-turn-helix motif. This is not always true, however, as in the case of the EF-hand. In biochemistry, the tertiary structure of a protein is its overall shape. ... A representation of the 3D structure of the Myoglobin protein. ... Structural biology is a branch of molecular biology concerned with the study of the architecture and shape of biological macromolecules--proteins and nucleic acids in particular—and what causes them to have the structures they have. ... oommen sir is a fool. ...

Other motifs, especially in proteins, consist of only a small number of amino acids, functional groups or functional atoms and do not depend on any secondary structure. These motifs are often directly involved in a protein's function. For example the catalytic triad made up of a serine, histidine, and aspartic acid is observed in the structures of the unrelated proteins trypsin and subtilisin. Three amino acid residues found inside the active site of certain proteases. ... Serine (IPA ), organic compound, one of the 20 amino acids commonly found in animal proteins. ... Histidine is one of the 20 most common natural amino acids present in proteins. ... Aspartic acid (Asp, D), also known as aspartate, the name of its anion, is one of the 20 natural proteinogenic amino acids which are the building blocks of proteins. ... Trypsin (EC 3. ... Subtilisin is a proteolytic enzyme obtained from . ...

Because the relationship between primary structure and tertiary structure is not straightforward, two biopolymers may share the same motif yet lack appreciable primary structure similarity. In other words, a structural motif does not need to be associated with a sequence motif. Also, the existence of a sequence motif does not necessarily imply a distinctive structure. In most DNA motifs, for example, it is assumed that the DNA of that sequence does not deviate from the normal "double helical" structure. A protein primary structure is a chain of amino acids. ... In genetics, a sequence motif is a nucleotide or amino-acid sequence pattern that is widespread and has, or is conjectured to have, a biological significance. ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ...

Structural motifs in proteins

 elements varies from one protein and the next. 

Examples of motif types in proteins

Greek-key motif.

• Beta ribbon:

Extremely common. Two antiparallel beta strands connected by a tight turn of a few amino acids between them. Image File history File links Size of this preview: 626 × 599 pixelsFull resolution (652 × 624 pixel, file size: 26 KB, MIME type: image/jpeg) File historyClick on a date/time to view the file as it appeared at that time. ... Image File history File links Size of this preview: 626 × 599 pixelsFull resolution (652 × 624 pixel, file size: 26 KB, MIME type: image/jpeg) File historyClick on a date/time to view the file as it appeared at that time. ...

• Greek key:

4 beta strands folded over into a sandwich shape. A simple Greek key design A Greek Key is a repeating design element used in architecture, jewelry and fabrics. ...

• Omega loop:

a loop where the residues that make up the beginning and end of the loop are very close together. The omega loop is a protein motif. ...

• Helix loop helix:

Consists of alpha helices bound by a looping stretch of amino acids. Important in DNA binding proteins. bHLH structural motif of the AhR protein: two α helices (blue) connected by a loop (red) A basic-helix-loop-helix (bHLH) is a protein structural motif that characterizes a family of transcription factors. ...

• Zinc finger:

Two beta strands with an alpha helix end folded over to bind a zinc ion. This motif is seen in transcription factors. Cartoon representation of the protein Zif268 (blue) containing three zinc fingers in complex with DNA (orange). ...

See also: structural domain

• Helix-turn-helix:

• Beta hairpin:

Within a protein, a structural domain (domain) is an element of overall structure that is self-stabilizing and often folds independently of the rest of the protein chain. ... The λ repressor of bacteriophage lambda employs a helix-turn-helix to bind DNA. In proteins, the helix-turn-helix (HTH) is a major structural motif capable of binding DNA. It is composed of two α helices joined by a short strand of amino acids and is found in many... Cartoon representation of a β-hairpin The beta hairpin (or beta-beta unit) structural motif is the simplest protein motif involving two beta strands. ...

See also

• Motif domain

Protein binding motif is a short protein sequence motif that interacts with other proteins. ...

References

• Prosite Database of protein families and domains
• SCOP Structural classification of Proteins
• CATH Class Architecture Topology Homology
• FSSP FSSP
• PASS2 PASS2 - Protein Alignments as Structural Superfamilies
• SMoS SMoS - Database of Structural Motifs of Superfamily