Editing Protein engineering (section)

== Screening and selection techniques ==
Once a protein has undergone directed evolution, ration design or semi-ration design, the libraries of mutant proteins must be screened to determine which mutants show enhanced properties. Phage display methods are one option for screening proteins. This method involves the fusion of genes encoding the variant polypeptides with phage coat protein genes. Protein variants expressed on phage surfaces are selected by binding with immobilized targets in vitro. Phages with selected protein variants are then amplified in bacteria, followed by the identification of positive clones by enzyme linked immunosorbent assay. These selected phages are then subjected to DNA sequencing.<ref name=PoluriBook/>{{page needed|date=May 2017}}

Cell surface display systems can also be utilized to screen mutant polypeptide libraries. The library mutant genes are incorporated into expression vectors which are then transformed into appropriate host cells. These host cells are subjected to further high throughput screening methods to identify the cells with desired phenotypes.<ref name=PoluriBook/>{{page needed|date=May 2017}}

Cell free display systems have been developed to exploit ''in vitro'' protein translation or cell free translation. These methods include mRNA display, ribosome display, covalent and non covalent DNA display, and ''in vitro'' compartmentalization.<ref name=PoluriBook/>{{rp|53}} 

===Enzyme engineering===
Enzyme engineering is the application of modifying an enzyme's structure (and, thus, its function) or modifying the catalytic activity of isolated [[enzyme]]s to produce new metabolites, to allow new (catalyzed) pathways for reactions to occur,<ref>{{cite news |title='Designer Enzymes' Created By Chemists Have Defense And Medical Uses |url=https://www.sciencedaily.com/releases/2008/03/080319160050.htm |work=ScienceDaily |date=March 20, 2008 }}</ref> or to convert from certain compounds into others ([[biotransformation]]). These products are useful as chemicals, pharmaceuticals, fuel, food, or agricultural additives.

An ''enzyme reactor'' <ref>{{cite web |url=http://www.lsbu.ac.uk/biology/enztech/reactors.html |title=Enzyme reactors |access-date=2013-11-02 |url-status=dead |archive-url=https://web.archive.org/web/20120502110325/http://www.lsbu.ac.uk/biology/enztech/reactors.html |archive-date=2012-05-02 }}</ref> consists of a vessel containing a reactional medium that is used to perform a desired conversion by enzymatic means. Enzymes used in this process are free in the solution. Also Microorganisms are one of important origin for genuine enzymes .<ref>{{Cite journal |last1=Sharma |first1=Anshula |last2=Gupta |first2=Gaganjot |last3=Ahmad |first3=Tawseef |last4=Mansoor |first4=Sheikh |last5=Kaur |first5=Baljinder |date=2021-02-17 |title=Enzyme Engineering: Current Trends and Future Perspectives |url=https://doi.org/10.1080/87559129.2019.1695835 |journal=Food Reviews International |volume=37 |issue=2 |pages=121–154 |doi=10.1080/87559129.2019.1695835 |s2cid=213299369 |issn=8755-9129|url-access=subscription }}</ref>