Ternary complex

{{short description|Protein complex among three different molecules}}

{{Refimprove|date=January 2010}}

A ternary complex is a protein complex containing three different molecules that are bound together. In structural biology, ternary complex can also be used to describe a crystal containing a protein with two small molecules bound, such as a cofactor and a substrate; or a complex formed between two proteins and a single substrate.{{Cite book|title=Protein methyltransferass |first1=Steven G. |last1=Clar|first2=Fuyuhiko |last2=Tamanoi |pages=162–172 |publisher=Academic Press|year=2006|isbn=978-0-12-122725-8}} In Immunology, ternary complex can refer to the MHC–peptide–T-cell-receptor complex formed when T cells recognize epitopes of an antigen.

Another important example is the ternary complex formed during eukaryotic translation, in which ternary complex composed of eIF2 + GTP + Met-tRNA_i^Met is formed.{{Cite journal |last1=Robert |first1=Francis |last2=Kapp |first2=Lee D. |last3=Khan |first3=Shakila N. |last4=Acker |first4=Michael G. |last5=Kolitz |first5=Sarah |last6=Kazemi |first6=Shirin |last7=Kaufman |first7=Randal J. |last8=Merrick |first8=William C. |last9=Koromilas |first9=Antonis E. |last10=Lorsch |first10=Jon R. |last11=Pelletier |first11=Jerry |date=November 2006 |editor-last=Schmid |editor-first=Sandra |title=Initiation of Protein Synthesis by Hepatitis C Virus Is Refractory to Reduced eIF2 · GTP · Met-tRNA i Met Ternary Complex Availability |journal=Molecular Biology of the Cell |language=en |volume=17 |issue=11 |pages=4632–4644 |doi=10.1091/mbc.e06-06-0478 |issn=1059-1524 |pmc=1635388 |pmid=16928960}}

A ternary complex can be a complex formed between two substrate molecules and an enzyme. This is seen in multi-substrate enzyme-catalyzed reactions where two substrates and two products can be formed. The ternary complex is an intermediate species in this type of enzyme-catalyzed reaction. An example for a ternary complex is seen in the random-order mechanism or the compulsory-order mechanism of enzyme catalysis for multiple substrates.{{Cite journal |last1=Hindson |first1=V. John |last2=Shaw |first2=William V. |date=2003-03-01 |title=Random-Order Ternary Complex Reaction Mechanism of Serine Acetyltransferase from Escherichia coli |url=https://pubs.acs.org/doi/10.1021/bi0267893 |journal=Biochemistry |language=en |volume=42 |issue=10 |pages=3113–3119 |doi=10.1021/bi0267893 |pmid=12627979 |issn=0006-2960|url-access=subscription }}

The term ternary complex can also refer to a polymer formed by electrostatic interactions.{{Cite book|title=Trends in colloid and interface science XVII |first1=Valérie |last1=Cabuil |first2=Pierre |last2=Levitz |first3=Clande |last3=Treiner |publisher=Springer |page=45 |year=2004 |isbn=978-3-540-20073-4}}