Crystal Structure of Human Protein-tyrosine Phosphatase SHP-1

Abstract

SHP-1 is a cytosolic protein-tyrosine phosphatase that behaves as a negative regulator in eukaryotic cellular signaling pathways. To understand its regulatory mechanism, we have determined the crystal structure of the C-terminal truncated human SHP-1 in the inactive conformation at 2.8-Å resolution and refined the structure to a crystallographic R-factor of 24.0%. The three-dimensional structure shows that the ligand-free SHP-1 has an auto-inhibited conformation. Its N-SH2 domain blocks the catalytic domain and keeps the enzyme in the inactive conformation, which supports that the phosphatase activity of SHP-1 is primarily regulated by the N-SH2 domain. In addition, the C-SH2 domain of SHP-1 has a different orientation from and is more flexible than that of SHP-2, which enables us to propose an enzymatic activation mechanism in which the C-SH2 domains of SHPs could be involved in searching for phosphotyrosine activators.Tyrosine phosphorylation is a key mechanism for regulating eukaryotic cellular signaling pathways. The protein tyrosine phosphorylation level is precisely regulated by two types of enzymes: protein-tyrosine kinases (PTKs) 1 and protein-tyrosine phosphatases (PTPs), in which PTPs act to counter-balance the process through dephosphorylation of the phosphorylated tyrosines (1, 2). PTPs can be divided into two groups, receptor protein-tyrosine phosphatases and cytosolic proteintyrosine phosphatases. The SH2 domain-containing PTPs, SHP-1 and SHP-2, are both cytosolic PTPs and share many structural and regulatory features. They both have two tandem SH2 domains at the N terminus followed by a single catalytic domain and an inhibitory C-terminal tail. However, irrespective of similar structural and regulatory characteristics, these two enzymes have different biological function in vivo.Different from SHP-2, which is expressed in all kinds of tissues, SHP-1 is predominantly expressed in hematopoietic and epithelial cells and behaves mainly as a negative regulator of signaling pathways in lymphocytes (1, 2). SHP-1 is dormant in the cytosol, with its phosphatase activity inhibited by both the SH2 domains and the C-terminal tail (1,(3)(4)(5). In response to an activation signal, SHP-1 is recruited to membrane-bound inhibitory receptors via the binding of its SH2 domains to the tyrosine-phosphorylated immunoreceptor tyrosine-based inhibitory motif within the cytoplasmic domain of a receptor (6 -8). During this process, SHP-1 undergoes a structural rearrangement, exposes its active site, and binds to the downstream substrates, thereby dephosphorylating the substrates to turn off the cellular signals.SHP-1 also presents in several types of non-hematopoietic cells (9 -12). Overexpression of a catalytically inactive SHP-1 mutant in these cells strongly suppressed mitogen-activated pathways, reducing signal transduction and activation of transcription; these findings demonstrate that SHP-1 has a positive effect on mitogenic signaling in these non-hematopoietic cells (10, 11). Thus, SHP-1 probably has both the nega...

The Protein-tyrosine Phosphatase SHP-1 Associates with the Phosphorylated Immunoreceptor Tyrosine-based Activation Motif of FcγRIIa to Modulate Signaling Events in Myeloid Cells

“…Activation of SHP-1 enzyme requires the engagement of its NH 2 -terminal SH2 domain with phosphotyrosines to relieve the intramolecular constraint placed on the phosphatase domain (26). Consistent with this notion, our results suggest that the engagement of SHP-1 by the NH 2 -terminal ITAM tyrosine of Fc␥RIIa leads to the activation of SHP-1.…”

Inflammation and autoimmunity caused by a SHP1 mutation depend on IL-1, MyD88, and a microbial trigger

“…The spin mutation occurs in the C-terminal SH2 domain, within the BG loop that forms part of the binding interface with pY ϩ 1 and pY ϩ 3 residues. The N-terminal SH2 domain is thought to undergo a conformational change that unblocks the catalytic domain upon engagement, allowing phosphatase activation (19)(20)(21). The C-terminal SH2 domain is not required for this disinhibition, but its presence is indispensable for optimal SHP signaling, and it has been proposed to aid in recruitment of binding partners.…”

Blocking the Function of Tyrosine Phosphatase SHP-2 by Targeting Its Src Homology 2 Domains

“…Because the specific functions of SHP-1 and SHP-2 are defined by both catalytic and SH2 domains, inhibitors can target the SH2 domains as well as the catalytic domains. Determination of the crystal structures revealed very high structural similarity between SHP-1 and SHP-2, especially in the catalytic and N-SH2 domains (12,13). Both SHP-1 and SHP-2 use the N-SH2 domain to keep the enzymes in the inactive conformation.…”

“…The catalytic domains of all classic protein-tyrosine phosphatases (PTPs) share extremely high similarity in ternary structures. In fact, the catalytic domains of SHP-2 and its closest homologue SHP-1 share 60% sequence identity, but the ternary structures of the two catalytic domains are almost superimposible (11)(12)(13). This makes it difficult to find highly selective inhibitors targeting the catalytic domains.…”

“…This low level of activity is because of an internal suppression because the enzymes are significantly activated by removal of either C-terminal segments or SH2 domains (14,15), by interaction with anionic phospholipids (15)(16)(17), and by binding of SH2 domains to specific phosphopeptides (18,19). Furthermore, x-ray crystal structures of SHP-1 and SHP-2 reveal blocking of the catalytic center by the N-terminal SH2 domains (12,13). In vivo, SHP-1 and SHP-2 reside mainly in the cytosol where they are presumably inactive.…”