Editing Lectin (section)

==Biological functions==
Lectins may [[Glycan-protein interactions|bind]] to a soluble carbohydrate or to a carbohydrate [[functional group|moiety]] that is a part of a [[glycoprotein]] or [[glycolipid]]. They typically [[Agglutination (biology)|agglutinate]] certain animal cells and/or precipitate [[glycoconjugate]]s. Most lectins do not possess [[enzymatic]] activity.

[[File:gs4 sugar all.png|thumb|An [[oligosaccharide]] (shown in grey) bound in the binding site of a plant lectin (''[[Griffonia simplicifolia]]'' isolectin IV in complex with the Lewis b [[blood group]] determinant); only a part of the oligosaccharide (central, in grey) is shown for clarity.]]

===Animals===
Lectins have these functions in animals:
* The regulation of [[cell adhesion]]
* The regulation of [[glycoprotein]] synthesis
* The regulation of blood protein levels
* The binding of soluble extracellular and intercellular glycoproteins
* As a receptor on the surface of mammalian liver cells for the recognition of [[galactose]] residues, which results in removal of certain glycoproteins from the circulatory system
* As a receptor that recognizes hydrolytic enzymes containing [[mannose-6-phosphate]], and targets these proteins for delivery to the [[lysosome]]s; [[I-cell disease]] is one type of defect in this particular system.
* Lectins are known to play important roles in the innate [[immune system]]. Lectins such as the [[mannose-binding lectin]], help mediate the first-line defense against invading [[microorganisms]]. Other immune lectins play a role in self-nonself discrimination and they likely modulate inflammatory and autoreactive processes.<ref>{{cite journal |vauthors=Maverakis E, Kim K, Shimoda M, Gershwin M, Patel F, Wilken R, Raychaudhuri S, Ruhaak LR, Lebrilla CB |title=Glycans in the immune system and The Altered Glycan Theory of Autoimmunity |journal=J Autoimmun |volume=57 |issue=6 |pages=1–13 |year=2015 |pmid=25578468 |pmc=4340844 |doi=10.1016/j.jaut.2014.12.002}}</ref> [[Intelectin]]s (X-type lectins) bind microbial glycans and may function in the innate immune system as well. Lectins may be involved in pattern recognition and pathogen elimination in the innate immunity of vertebrates including fishes.<ref>{{cite journal |doi=10.1016/j.molimm.2013.06.020 |pmid=23911406 |title=Fish lily type lectin-1 contains β-prism architecture: Immunological characterization |journal=Molecular Immunology |volume=56 |issue=4 |pages=497–506 |year=2013 |last1=Arasu |first1=Abirami |last2=Kumaresan |first2=Venkatesh |last3=Sathyamoorthi |first3=Akila |last4=Palanisamy |first4=Rajesh |last5=Prabha |first5=Nagaram |last6=Bhatt |first6=Prasanth |last7=Roy |first7=Arpita |last8=Thirumalai |first8=Muthukumaresan Kuppusamy |last9=Gnanam |first9=Annie J.|last10=Pasupuleti|first10=Mukesh |last11=Marimuthu |first11=Kasi |last12=Arockiaraj |first12=Jesu}}</ref>

===Plants===
The function of lectins in plants ([[legume lectin]]) is still uncertain. Once thought to be necessary for [[rhizobia]] binding, this proposed function was ruled out through lectin-knockout [[transgene]] studies.<ref>{{Cite journal |title=Coordinating Nodule Morphogenesis with Rhizobial Infection in Legumes |journal=Annual Review of Plant Biology |volume=59 |pages=519–546 |doi=10.1146/annurev.arplant.59.032607.092839 |pmid=18444906 |year=2008 |last1=Oldroyd |first1=Giles E.D. |last2=Downie |first2=J. Allan}}</ref>

The large concentration of lectins in plant seeds decreases with growth, and suggests a role in plant [[germination]] and perhaps in the seed's survival itself. The binding of glycoproteins on the surface of parasitic cells also is believed to be a function. Several plant lectins have been found to recognize noncarbohydrate [[ligands]] that are primarily [[hydrophobic]] in nature, including [[adenine]], [[auxins]], [[cytokinin]], and [[indole acetic acid]], as well as water-soluble [[porphyrins]]. These interactions may be physiologically relevant, since some of these molecules function as [[phytohormone]]s.<ref name="pmid16525538">{{cite journal |vauthors=Komath SS, Kavitha M, Swamy MJ |title=Beyond carbohydrate binding: new directions in plant lectin research |journal=Org. Biomol. Chem. |volume=4 |issue=6 |pages=973–988 |date=March 2006 |pmid=16525538 |doi=10.1039/b515446d}}</ref>

Lectin receptor kinases (LecRKs) are believed to recognize damage associated molecular patterns (DAMPs), which are created or released from herbivore attack.{{cn|date=May 2021}} In ''[[Arabidopsis]]'', legume-type LecRKs Clade 1 has 11 LecRK proteins. LecRK-1.8 has been reported to recognize extracellular [[Nicotinamide adenine dinucleotide|NAD]] molecules and LecRK-1.9 has been reported to recognize extracellular [[Adenosine triphosphate|ATP]] molecules.{{cn|date=May 2021}}

Extraction of proteins and lectins can be extracted via similar processes, also with their analysis, and discovery. For example [[cottonseed]]  contains compounds of interest within the studies of extraction and purification of proteins<ref> L.Y. Yatsu, T.J. Jacks, "Association of lysosomal activity with aleurone grains in plant seeds", ''Archives of Biochemistry and Biophysics'', Vol. 124, 1968, pp. 466–471, {{ISSN|0003-9861}}, {{doi|10.1016/0003-9861(68)90354-8}}.</ref>

===Bacteria and viruses===
Some [[hepatitis C]] viral glycoproteins may attach to [[C-type lectin]]s on the host cell surface (liver cells) to initiate infection.<ref>{{cite journal |author=R. Bartenschlager |author2=S. Sparacio |title=Hepatitis C Virus Molecular Clones and Their Replication Capacity in Vivo and in Cell Culture |journal=Virus Research |volume=127 |issue=2 |pages=195–207 |year=2007 |doi=10.1016/j.virusres.2007.02.022 |pmid=17428568}}</ref> To avoid clearance from the body by the [[innate immune system]], pathogens (e.g., [[virus]] particles and [[bacteria]] that infect human cells) often express surface lectins known as [[adhesins]] and [[hemagglutinin]]s that bind to tissue-specific [[glycans]] on host cell-surface glycoproteins and [[glycolipids]].<ref>{{cite journal |pmid=9973330 |pmc=93481 |title=Bacterial adhesins: common themes and variations in architecture and assembly |journal=J Bacteriol |volume=181 |issue=4 |pages=1059–1071 |year=1999 |last1=Soto |first1=GE |last2=Hultgren |first2=SJ |doi=10.1128/JB.181.4.1059-1071.1999}}</ref> Multiple viruses, including [[influenza]] and several viruses in the [[Paramyxoviridae]] family, use this mechanism to bind and gain entry to target cells.<ref>{{Cite journal| doi = 10.1128/JVI.76.24.13028-13033.2002| issn = 0022-538X| volume = 76| issue = 24| pages = 13028–13033| last1 = Takimoto| first1 = Toru| last2 = Taylor| first2 = Garry L.| last3 = Connaris| first3 = Helen C.| last4 = Crennell| first4 = Susan J.| last5 = Portner| first5 = Allen| title = Role of the Hemagglutinin-Neuraminidase Protein in the Mechanism of Paramyxovirus-Cell Membrane Fusion| journal = Journal of Virology| date = 2002| pmid = 12438628| pmc = 136693}}</ref>