:Helper-component proteinase

{{Infobox enzyme

| Name = Helper-component proteinase

| EC_number = 3.4.22.45

| CAS_number = 124566-20-7

| GO_code =

| image =

| width =

| caption =

}}

Helper-component proteinase ({{EC number|3.4.22.45}}, HC-Pro) is an enzyme.{{cite journal | vauthors = Kasschau KD, Carrington JC | title = Requirement for HC-Pro processing during genome amplification of tobacco etch potyvirus | journal = Virology | volume = 209 | issue = 1 | pages = 268–73 | date = May 1995 | pmid = 7747479 | doi = 10.1006/viro.1995.1254 | doi-access = free }}{{cite book | chapter = Potyvirus helper component proteinase | title = Handbook of Proteolytic Enzymes |author1 = Verchot, J. |year = 1998 |pages = 677–679 |editor = Barrett, A.J. |editor2 =Rawlings, N.D. |editor3 =Woessner, J.F. |publisher = Handbook of Proteolytic Enzymes |location = London }} This enzyme catalyses the following chemical reaction

: Hydrolyses a Gly-Gly bond at its own C-terminus, commonly in the sequence -Tyr-Xaa-Val-Gly-Gly, in the processing of the potyviral polyprotein

This enzyme is present in plant RNA viruses of the Potyviridae family. HC-Pro is encoded by all potyviruses, but is absent in some members of the Ipomovirus genus.{{Cite journal |last1=Pasin |first1=Fabio |last2=Daròs |first2=José-Antonio |last3=Tzanetakis |first3=Ioannis E |title=Proteome expansion in the Potyviridae evolutionary radiation |journal=FEMS Microbiology Reviews |year=2022 |volume=46 |issue=4 |language=en |pages=fuac011 |doi=10.1093/femsre/fuac011 |pmid=35195244 |pmc=9249622 |issn=1574-6976}} HC-Pro is involved in virus transmission, virus polyprotein processing, and suppression of RNA silencing, an antiviral mechanism of plants.{{Cite journal |last1=Valli |first1=Adrián A. |last2=Gallo |first2=Araiz |last3=Rodamilans |first3=Bernardo |last4=López-Moya |first4=Juan José |last5=García |first5=Juan Antonio |date=March 2018 |title=The HCPro from the Potyviridae family: an enviable multitasking Helper Component that every virus would like to have: The HCPro from the Potyviridae family |journal=Molecular Plant Pathology |language=en |volume=19 |issue=3 |pages=744–763 |doi=10.1111/mpp.12553 |pmc=6638112 |pmid=28371183}}