The beta12-beta13 loop is a key regulatory element for the activity and properties of the catalytic domain of protein phosphatase 1 and 2B

Calcineurin Undergoes a Conformational Switch Evoked via Peptidyl-Prolyl Isomerization

A limited repertoire of PPP family of serine/threonine phosphatases with a highly conserved catalytic domain acts on thousands of protein targets to orchestrate myriad central biological roles. A major structural reorganization of human calcineurin, a ubiquitous Ser/Thr PPP regulated by calcium and calmodulin and targeted by immunosuppressant drugs cyclosporin A and FK506, is unveiled here. The new conformation involves trans- to cis-isomerization of proline in the SAPNY sequence, highly conserved across PPPs, and remodels the main regulatory site where NFATc transcription factors bind. Transitions between cis- and trans-conformations may involve peptidyl prolyl isomerases such as cyclophilin A and FKBP12, which are known to physically interact with and modulate calcineurin even in the absence of immunosuppressant drugs. Alternative conformations in PPPs provide a new perspective on interactions with substrates and other protein partners and may foster development of more specific inhibitors as drug candidates.

Protein phosphatase PP1 negatively regulates the Toll-like receptor- and RIG-I-like receptor-triggered production of type I interferon by inhibiting IRF3 phosphorylation at serines 396 and 385 in macrophage

The production of type I interferon must be tightly regulated, and the aberrant production of this protein is harmful or even fatal to the host. The transcription factor IRF3 phosphorylation is a central regulator of type I interferon meditated antiviral response. Protein phosphatase-1 (PP1) has been reported to be important in many cell functions, including development, differentiation, and tumorigenesis. However, the roles of PP1 in Toll-like receptor (TLR)- or retinoic acid-inducible gene I like receptor (RLR)-triggered IRF-3 activation remain unclear. Here, we show that the activity of PP1 is downregulated in macrophages upon stimulation with TLR or RLR ligands, including lipopolysaccharide, and poly(I:C), or vesicular stomatitis virus (VSV), respectively. The overexpression of PP1 selectively inhibits TLR- and VSV-induced interferon regulatory factor 3 (IRF3) activation but has no substantial effect on TANK-binding kinase 1 (TBK1),ΚB kinase ε (IKKε) activation. Conversely, RNA interference of PP1 significantly promotes IRF3 activation. Consistently, The overexpression of PP1 inhibits TLR- and VSV-triggered IFN-β production while PP1 knockdown significantly increases the production of IFN-β in macrophages. We further demonstrate that PP1 directly interacts with IRF3 and dephosphorylates IRF3 at Ser385 and Ser396, resulting in the suppression of TLR- and RLR-triggered IFN-β production. Thus, PP1 functions as a negative feedback regulator of TLR- and RLR-triggered antiviral immune responses by acting as an IRF3 phosphatase.

Mechanism of activation of Saccharomyces cerevisiae calcineurin by Mn2+

Saccharomyces cerevisiae calcineurin (CN) consists of a catalytic subunit CNA1 or CNA2 and a regulatory subunit CNB1. The kinetics of activation of yeast CN holoenzymes and their catalytic domains by Mn2+ were investigated. We report that the in vitro phosphatase reaction activated by Mn2+ typically has a pronounced initial lag phase caused by slow conformational rearrangement of the holoenzyme-Mn2+. A similar lag phase was detected using just the catalytic domain of yeast CN, indicating that the slowness of Mn2+-induced conformational change of CN results from a rearrangement within the catalytic domain. The Mn2+-activation of CN was reversible. The dissociation constant of the CN heterodimer containing the CNA2 subunit in the presence of Mn2+ was 3-fold higher than that of CN containing the CNA1 subunit and that of the catalytic domains of CNA1 and CNA2, pointing to differences between the residues surrounding the Mn2+-binding sites of CNA1 and CNA2.

The nonconserved N-terminus of protein phosphatases 1 influences its active site

Protein phosphatase 1 consists of a secondary structure arrangement, conserved in the serine/threonine protein phosphatase gene family, flanked by nonconserved N-terminal and C-terminal domains. The deletion mutant of PP1 with the 8 nonconserved N-terminal residues removed was designated PP1-(9-330). PP1-(9-330) had a higher activity and affinity than PP1 when assayed against four different substrates, and it also demonstrated a 6-fold higher sensitivity to the inhibitor okadaic acid. This suggested that the N-terminal domain suppressed the activity of PP1 and interfered with its inhibition by okadaic acid. The ANS fluorescence intensity of PP1-(9-330) was greater than that of PP1, which implies that the hydrophobic groove running from active site in the truncated PP1 was more hydrophobic than in PP1. Our findings provide evidence that the nonconserved N-terminus of PP1 functions as an important regulatory domain that influences the active site and its pertinent properties.

The N-terminal domain influences the structure and property of protein phosphatase 1

The protein phosphatase 1 has conserved cores in PPP gene family flanked by non-conserved N-terminal domains. PP1 with residues 1-8 deleted or substituted by residues 1-42 of calcineurin catalytic subunit were designated PP1-(9-330) and CNA(1-42)-PP1(9-330), respectively. When compared with PP1, PP1-(9-330) had higher and CNA(1-42)-PP1(9-330) had lower activity with three kinds of substrates; PP1-(9-330) has higher and CNA(1-42)-PP1(9-330) has lower sensitivity to okadaic acid. These results imply that the N-terminal residues influence the activity and sensitivity to inhibitors of PP1. PP1-(9-330), PP1, and CNA(1-42)-PP1(9-330) displayed increasing K (m) and decreasing V (max) with three kinds of substrates, which suggest that the N-terminal residues are connected with the substrates affinity and catalytic efficiency of PP1. PP1-(9-330) has higher and CNA(1-42)-PP1(9-330) has lower fluorescence intensity than PP1, and the emission wavelength maximum was blue-shifted from PP1 to PP1-(9-330) and red-shifted from PP1 to CNA(1-42)-PP1(9-330). Our findings provide evidence that the N-terminal domain is an important region influencing the structure and properties of PP1.