View source for Ligase

{{Short description|Class of enzymes that can form bonds between molecules}}
{{Distinguish|Lipase}}
{{About|general ligases|DNA specific ligases|DNA ligase}}
{{Use mdy dates|date=July 2013}}

In [[biochemistry]], a '''ligase''' is an [[enzyme]] that can [[catalyze]] the joining ([[Ligation (molecular biology)|ligation]]) of two molecules by forming a new [[chemical bond]]. This is typically via [[hydrolysis]] of a small pendant chemical group on one of the molecules, typically resulting in the formation of new C-O, C-S, or C-N bonds. For example, [[DNA ligase]] can join two complementary fragments of nucleic acid by forming phosphodiester bonds, and repair single stranded breaks that arise in double stranded DNA during replication.

In general, a ligase catalyzes the following dehydration reaction, thus joining molecules A and B:

A-OH + B-H → A–B + H<sub>2</sub>O

==Nomenclature==
The naming of ligases is inconsistent and so these enzymes are commonly known by several different names. Generally, the common names of ligases include the word "ligase", such as in [[DNA ligase]], an enzyme commonly used in molecular biology [[Laboratory|laboratories]] to join together [[DNA]] fragments. However, many common names use the term "synthetase" or "synthase" instead, because they are used to [[Biosynthesis|synthesize]] new molecules.<ref>{{Cite web |title=IntEnz - EC 6 |url=https://www.ebi.ac.uk/intenz/query?cmd=SearchEC&ec=6#:~:text=EC%206%20-%20Ligases&text=Ligases%20are%20enzymes%20that%20catalyse,or%20%27carboxylase%27%20is%20used. |access-date=2023-05-02 |website=www.ebi.ac.uk}}</ref> There are also some ligases that use the name "carboxylase" to indicate that the enzyme specifically catalyzes a [[carboxylation]] reaction.

To note: biochemical nomenclature has sometimes distinguished synthetases from [[synthase]]s and sometimes treated the words as [[synonym]]s.<ref>{{Cite web |title=Synthetases - Ligases - Enzymes - Products |url=https://www.axonmedchem.com/products/enzymes/ligases/synthetases#:~:text=Originally,%20biochemical%20nomenclature%20distinguished%20synthetases,synthetases%20do%20use%20nucleoside%20triphosphates. |access-date=2023-05-02 |website=www.axonmedchem.com}}</ref> Commonly, the two terms are used interchangeably and are both used to describe ligases.

==Classification==
Ligases are classified as '''EC 6''' in the [[Enzyme Commission number|EC number]] classification of enzymes. Ligases can be further classified into six subclasses:

*[[:Category:EC 6.1|EC 6.1]] includes ligases used to form carbon-oxygen bonds
*[[:Category:EC 6.2|EC 6.2]] includes ligases used to form carbon-sulfur bonds
*[[:Category:EC 6.3|EC 6.3]] includes ligases used to form carbon-nitrogen bonds (including [[argininosuccinate synthetase]])
*[[:Category:EC 6.4|EC 6.4]] includes ligases used to form carbon-carbon bonds, such as [[acetyl-CoA carboxylase]]
*[[:Category:EC 6.5|EC 6.5]] includes ligases used to form [[phosphoric ester]] bonds, such as [[DNA ligase]]
*[[:Category:EC 6.6|EC 6.6]] includes ligases used to form nitrogen-metal bonds, as in the [[chelatase]]s

==Membrane-associated ligases==
Some ligases associate with [[biological membranes]] as [[peripheral membrane protein]]s or anchored through a single [[transmembrane helix]],<ref>[http://membranome.org/protein_classes/14 Superfamilies of single-pass transmembrane ligases] in [[Membranome database]]</ref> for example certain [[ubiquitin ligase]] related proteins.

==Etymology and pronunciation==
The word ''ligase'' uses [[classical compound|combining forms]] of ''[[wikt:lig-#Prefix|lig-]]'' (from the [[Latin language|Latin]] verb ''ligāre'', "to bind" or "to tie together") + ''[[wikt:-ase#Suffix|-ase]]'' (denoting an enzyme), yielding "binding enzyme".

==See also==
{{Portal|Chemistry}}
*[[DNA ligase]]
*[[Acetyl-CoA carboxylase]]
*[[Nuclease]]
*[[Protease]]
*[[Ubiquitin ligase]]

==References==
{{Reflist}}
* [https://web.archive.org/web/20110816091739/http://www.chem.qmul.ac.uk/iubmb/enzyme/EC6/intro.html EC 6 Introduction] from the Department of Chemistry at [[Queen Mary, University of London]]

{{Enzymes}}
{{Ligases}}
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[[Category:Ligases| ]]