Parvin: Difference between revisions

<StructureSection load='2vzc' size='450' side='right' scene='Alpha-parvin/Cv/1' caption='Human C-terminal domain of α-parvin complex with MPD, glycerol and TRS (PDB code [[2vzc]])'>

===Focal adhesions and cell migration===

Alpha-parvin possesses 6 putative proline-directed serine/threonine phosphorylation targets (residues 4, 8, 14, 16, 19, 61), of which serines 4 and 8 were shown to be the most important. Phosphorylation of alpha-parvin at serines 4 and 8 is correlated with the tightly regulated process of FA turnover during cell migration. Firstly, phosphorylation of these residues by cyclin B1/cdc2 is observed in the context of mitosis, whereby it contributes to FA disassembly required for cell-rounding prior to cell division, suggesting it may cause a similar effect during cell migration.<ref>PMID: 11931650</ref> Indeed, in migrating cells these residues are observed to be phosphorylated<ref>PMID: 15353548</ref>, likely as a result of MAP kinase<ref>PMID: 14636584</ref> and/or [[PI3K]]<ref>PMID: 12960424</ref>. Secondly, phosphomimetic mutations of serines 4 and 8 to aspartates result in faster migration and spreading, while mutations preventing phosphorylation impair these processes.<ref>PMID: 15353548</ref> Finally, as has already been mentioned in the introduction, knock-out mice phenotype (embryonic lethality due to severe cardiovascular defects) suggests alpha-parvin deficiency results in impaired directional migration of endothelial cells during embryonic development, heart development in particular.<ref>PMID: 19798050</ref> The macroscopic effects of alpha-parvin phosphorylation likely result from the altered affinity for its binding partners. So far it has been demonstrated that phosphorylation at serines 4 and 8 affects binding of alpha-parvin to TESK1 and CdGAP. When TESK1 is bound to alpha-parvin it is prevented from severing actin fibres. TESK1 is thought to be released from inhibition upon alpha-parvin phosphorylation and this can contribute to the decomposition of actin fibres and FA disassembly.<ref>PMID: 15817463</ref> CdGAP, on the other hand, is involved in the regulation of small GTPase signalling, which accounts for changes in cytoskeletal contractability during cell migration.<ref>PMID: 16860736</ref> Evidence suggesting that also the interaction with ILK is affected by phosphorylation is not strong<ref>PMID: 15872073</ref><ref>PMID: 12960424</ref>, but it is likely that this or yet other binding partners bind in the phosphorylation-dependent manner.

===Domain composition===

Alpha-parvin's structure can be divided into four regions: 1) N-terminal flexible domain (residues 1-96), 2) N-terminal CH domain (97-200 according to SMART<ref>PMID: 9600884</ref>), 3) linker region (201-241) and 4) C-terminal CH domain (242-372 identified by limited subtilisin proteolysis<ref>PMID: 18940607</ref>). Most interactions of alpha-parvin are mapped to the C-terminal CH domain, but CdGAP and perhaps alphaPIX or other, yet unknown partners, interact with the N-terminal flexibile domain. This flexible domain seems to lack a well defined 3D structure and can therefore be classified as a putative [[Intrinsically Disordered Protein|intrinsically disordered]] region. The interactions of this regions with the binding partners are therefore likely to be characterized by relatively low affinity, but high affinity nonetheless.<ref>PMID: 19265676</ref> The abovementioned phosphorylation sites (serines 4 and 8) involved in focal adhesion regulation are located in this segment, which makes them so called disorder-enhanced phosphorylation sites.<ref>PMID: 14960716</ref><ref>PMID: 18388127</ref>

===ILK binding===

The <scene name='Alpha-parvin/Ilk_parvin/1'>scene on the left</scene> shows the complex ([[3kmw]]) of the kinase domain of integrin-linked kinase (ILK, red) bound to the C-terminal CH domain of alpha-parvin (blue). One can also see the molecule of ATP (green) and the space-fill representation of the magnesium atom (white). When we <scene name='Alpha-parvin/Ilk_parvin/2'>turn the structure</scene> so that the N-terminal helix (now orange) of the CH domain of alpha-parvin is pointing up, we can see that unlike paxillin LD motifs, ILK kinase domain does not bind to the N-terminal region of the CH domain, but rather near the <scene name='Alpha-parvin/Ilk_parvin/3'>long loop</scene> between helices αC and αE. Other parts of the CH domain are also involved in binding, leading to a high interface area (around 1900 Ų) characteristic of high-affinity complexes.<ref>PMID:20005845</ref> Interestingly, ILK, which was recently proved to lack kinase activity<ref>PMID:20005845</ref><ref>PMID: 20033063</ref>, binds alpha-parvin analogously to the way in which kinases bind their substrates, i.e. with its pseudoactive site. The binding is not dependent on the presence of ATP. On the ILK's side the binding is mediated primarily by <scene name='Alpha-parvin/Ilk_parvin/6'>one of the helices</scene> (αG) and a <scene name='Alpha-parvin/Ilk_parvin/5'>part of the activation loop</scene>. The complex formation is particularly dependent on <scene name='Alpha-parvin/Ilk_parvin/7'>methionine 402 and lysine 403</scene> in αG of ILK - if these two residues are mutated to alanines, the complex formation is completely abolished. These residues are involved in many interactions with alpha-parvin (one of them, a hydrogen bond to asparagine 280, is shown) or water molecules (one of them shown as a pink dot).

</StructureSection>