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 and ...

, a protein trimer is a macromolecular

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 very large molecule important to biophysical processes, such as a protein or nucleic acid. It is composed of thousands of covalently bonded atoms. Many macromolecules are polymers of smaller molecules called monomers. The ...

s like

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

s or

nucleic acid Nucleic acids are biopolymers, macromolecules, essential to all known forms of life. They are composed of nucleotides, which are the monomers made of three components: a 5-carbon sugar, a phosphate group and a nitrogenous base. The two main ...

s. A homotrimer would be formed by three identical

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

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

Collagen Collagen () is the main structural protein in the extracellular matrix found in the body's various connective tissues. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whol ...

is an example of homotrimeric protein. Porins usually arrange themselves in membranes as trimers.

Bacteriophage T4 tail fiber

Multiple copies of a polypeptide encoded by a

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

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 ...

allele An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chrom ...

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 Epistasis is a phenomenon in genetics in which the effect of a gene mutation is dependent on the presence or absence of mutations in one or more other genes, respectively termed modifier genes. In other words, the effect of the mutation is dep ...

. 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

Protein structure Protein complexes {{Protein-stub

Bacteriophage T4 tail fiber

See also

References