Protein tyrosine phosphatases (PTPs) are a group of enzymes that remove phosphate groups from phosphorylated tyrosine residues on proteins.

Functions

Together with tyrosine kinases, PTPs regulate the phosphorylation state of many important signalling molecules, such as the MAP kinase family.

PTPs are increasingly viewed as integral components of signal transduction cascades, despite little studied and ill-understood compared to Tyrosine Kinases.

PTPs have been implicated in regulation of many cellular processes, including, but not limited to:

• Cell growth
• Cellular differentiation
• Mitotic cycles
• Oncogenic transformation

Classification

On the basis of the primary structure of their catalytic domains, PTPs are divided into four distinct classes:^[1]

The class I PTPs, are the the largest group of PTPs with 99 members which can be further subdivided into 38 classical PTPs and 61 VH-1 like or dual specific phosphatases (DSPs). The class I classical PTPs can be futher subdivided into 21 receptor and 17 non receptor type PTPs. The DSPs can also be further subdivided, in this case into 7 subfamilies made up of 11 MAPK phosphatases (MPKs), 3 Slingshots, 3 PRLs, 4 CDC14s, 19 atypical DSPs, 5 Phosphatase and tensin homologs (PTENs) and 16 Myotubularins. The class II PTPs contain only one member, low-molecular-weight phosphotyrosine phosphatase (LMPTP). The Class III PTPs contains three members, CDC25 A, B and C and the class IV PTPs contains four members, Eya1-4. Links to all 107 members of the protein tyrosine phosphatase family can be found in the template at the bottom of this article.

Expression pattern

Individual PTPs may be expressed by all cell types or their expression may be strictly tissue specific. Most cells express 30% to 60% of all the PTPs, however hematopoietic and neuronal cells express a relatively higher number of PTPs in comparision to other cell types. T cells and B cells of hematopoietic origin express around 60 to 70 different PTPs. The expression of several PTPS is restricted to hematopoietic cells, for example LYP, SHP1, CD45 and HePTP.^[2]

External links

• PTP Summary and Relevant Publications at Monash University

References

1. ↑
2. ↑

• pp 886-887.

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