thumbnail, 400px, Trimeric form of a TNF-α mutant In

biochemistry Biochemistry, or biological chemistry, is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology, a ...

, a protein trimer is a

macromolecular A macromolecule is a "molecule of high relative molecular mass, the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of low relative molecular mass." Polymers are physi ...

complex Complex commonly refers to: * Complexity, the behaviour of a system whose components interact in multiple ways so possible interactions are difficult to describe ** Complex system, a system composed of many components which may interact with each ...

formed by three, usually non-covalently bound,

macromolecule A macromolecule is a "molecule of high relative molecular mass, the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of low relative molecular mass." Polymers are physi ...

s like

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

s or

nucleic acid Nucleic acids are large biomolecules that are crucial in all cells and viruses. They are composed of nucleotides, which are the monomer components: a pentose, 5-carbon sugar, a phosphate group and a nitrogenous base. The two main classes of nuclei ...

s. A protein trimer often occurs from the assembly of a protein's quaternary structure. The non-covalent interactions between the

hydrophobic In chemistry, hydrophobicity is the chemical property of a molecule (called a hydrophobe) that is seemingly repelled from a mass of water. In contrast, hydrophiles are attracted to water. Hydrophobic molecules tend to be nonpolar and, thu ...

and

hydrophilic A hydrophile is a molecule or other molecular entity that is attracted to water molecules and tends to be dissolved by water.Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon'' Oxford: Clarendon Press. In contrast, hydrophobes are n ...

regions on the

polypeptides Peptides are short chains of amino acids linked by peptide bonds. A polypeptide is a longer, continuous, unbranched peptide chain. Polypeptides that have a molecular mass of 10,000 Da or more are called proteins. Chains of fewer than twenty ami ...

units help to stabilize the quaternary structure. Since a protein trimer is composed of multiple polypeptide subunits, it is considered an

oligomer In chemistry and biochemistry, an oligomer () is a molecule that consists of a few repeating units which could be derived, actually or conceptually, from smaller molecules, monomers.Quote: ''Oligomer molecule: A molecule of intermediate relativ ...

. A homotrimer would be formed by three identical

molecule A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...

s. A heterotrimer would be formed by three different macromolecules. Type II

Collagen Collagen () is the main structural protein in the extracellular matrix of the connective tissues of many animals. It is the most abundant protein in mammals, making up 25% to 35% of protein content. Amino acids are bound together to form a trip ...

is an example of homotrimeric protein, while Type I collagen is an AAB-type heterotrimeric protein. An example of viral protein homotrimeric protein is

mammarenavirus ''Mammarenavirus'' is a genus of viruses in the family ''Arenaviridae''. The name is a portmanteau of mammal and the former name ''Arenavirus'', and differentiates it from the reptile-associated ''Reptarenavirus''. ''Arenavirus'' comes from the ...

of Z matrix protein. Porins usually arrange themselves in membranes as trimers. __TOC__

Bacteriophage T4 tail fiber

Multiple copies of a polypeptide encoded by a

gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...

often can form an aggregate referred to as a multimer. When a multimer is formed from polypeptides produced by two different

mutant In biology, and especially in genetics, a mutant is an organism or a new genetic character arising or resulting from an instance of mutation, which is generally an alteration of the DNA sequence of the genome or chromosome of an organism. It i ...

allele An allele is a variant of the sequence of nucleotides at a particular location, or Locus (genetics), locus, on a DNA molecule. Alleles can differ at a single position through Single-nucleotide polymorphism, single nucleotide polymorphisms (SNP), ...

s of a particular gene, the mixed multimer may exhibit greater functional activity than the unmixed multimers formed by each of the mutants alone. When a mixed multimer displays increased functionality relative to the unmixed multimers, the phenomenon is referred to as intragenic complementation. The distal portion of each of the bacteriophage T4 tail fibers is encoded by gene ''37'' and mutants defective in this gene undergo intragenic complementation. This finding indicated that the distal tail fibers are a multimer of the gene ''37'' encoded polypeptide. An analysis of the complementation data further indicated that the polypeptides making up the multimer were folded back on themselves in the form of a hairpin. A further high-resolution crystal structure analysis of the distal tail fiber indicated that the gene ''37'' polypeptides are present as a trimer and that each polypeptide of the trimer is folded back on itself in a hairpin configuration.Bartual SG, Otero JM, Garcia-Doval C, et al. Structure of the bacteriophage T4 long tail fiber receptor-binding tip. Proc Natl Acad Sci U S A. 2010;107(47):20287-20292.

References

{{DEFAULTSORT:Protein Trimer Protein structure Protein complexes

Bacteriophage T4 tail fiber

See also

References