sentence: The Class I PTPs are the largest family with 99 members , which can be further divided into the classical PTPs ( 38 members ) including the receptor PTPs ( PTPR ) ( 21 members ) and non receptor PTPs ( PTPN ) ( 17 members ) , and the dual specificity phosphatases ( DUSPs ) ( 61 members ) capable of dephosphorylating serine , threonine and tyrosine residues .