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''''''Protein kinase C related

kinase/Tofacitinib

(prostrate and ovarian

cancer)-4OTI''''''

==Introduction==

<Structure load='4OTI' applet size='[450,338]' frame='true' align='right' caption='4oti, cartoon representation' scene='48/483882/Polarity/2' />

Protein kinase C related kinase is a family of enzymes that is initiated by hydrolysis of inositol phospholipids. They transmit extracellular signals across membrane and helps regulate calcium ion dependent processes. <scene name='48/483882/4oti/1'>Protein kinase</scene> helps elucidate a lot of biochemical mechanism of signal transduction and makes it easier for us to understand protein cell-to-cell communication. <ref>"Studies and perspectives of protein kinase C." Science 233.4761 (1986): 305-312.</ref>

PRK1 is a component of Rho-GTPase, histone demethylase, androgen receptor, and histone demethylase signaling pathways and is involved in ovary and prostate cancer. A lot of PRK1 is expressed in cases of ovarian serous carcinoma. PRK1 is a family of AGC kinase enzymes. This group of enzymes has a C-terminal regulatory region. The C-tail helps regulate enzyme activity. The C-terminal can also recruit binding partners including PDK1. This phenylalanine region is the active-site tether and can connect to both nucleotide and inhibitors.

<ref>Nishizuka, Yasutomi. <ref name="rasmo">DOI: 10.1371/journal.pone.0103638</ref>

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==Overall Structure==

<Structure load='4OTI' applet size='[450,338]' frame='true' align='right' caption='4oti, Overall Structure' scene='48/483882/Polarity/2' />

4OTI is a single chain protein, comprised of 15 <font color='blue'>alpha helices </font> and 8 <font color='gold'>beta strands</font> shown <scene name='48/483882/Secondary_structures/1'>here </scene>. The beta strands form <scene name='48/483882/Betasheet/2'>two beta sheets</scene>, which are arranged antiparallel, giving added stability to the molecule, orienting its hydrogen bonds in a favorable manner. There are a total of 304 residues in the protein. <ref name="rasmol">PMID:25111382 </ref>

4oti can be divided into <scene name='48/483882/Loberegions/3'>two distinct regions</scene>, an <font color='orangered'>N terminal lobe region</font> providing regulation, and a <font color='deepskyblue'>C terminal lobe region</font> that proposes as a catalytic region. The N and C terminals are separated by a <font color='purple'>hinge region</font>, which can be adjusted when the enzyme is bound to a membrane. One key structural feature of 4oti is the <font color='red'>C-tail</font>, part of the <scene name='48/483882/Ctailk/1'>C-terminal regulatory region</scene>, which travels from the C lobe to a final position in front of the N lobe. The lobe regions are approximately 20-40 kDa and 45kDa in size respectively. <ref>Newton, A. C. (1995). Protein kinase C: structure, function, and regulation. J. Biol. Chem. 270, 28495-28498. </ref>

4oti's beta sheets reside in the N-lobe, and construct a <scene name='48/483882/Beta_sheet_pocket/1'>beta sheets pocket,</scene>, which serves as an open binding site for a ligand. <scene name='48/483882/Mi1_ligand/1'>4oti's ligand</scene> is known as MI1, and has a structural formula of C16H20N6O. <scene name='48/483882/Glu_ser/1'>MI1 bonds</scene> to the C-terminus of <font color='seagreen'>Glu702</font> and the N-terminus of <font color='crimson'>Ser704</font>, forming hydrogen bonds with Glu's carbonyl and Ser's nitrogen.

[[Image:mi1test.png]]

4oti's <scene name='48/483882/Active/3'>active site</scene> contains an additional <font color='blueviolet'>16 residues</font>, which are available for only non-binding interactions. <ref name="rasmol" /> Many of the <scene name='48/483882/Water/2'>the exposed side chains</scene> of otherwise <font color='seagreen'>buried residues</font>, such as

<font color='black'>'''Glu702'''</font> serve as binding sites for interactions with <font color='magenta'>water</font>.

<font color=''></font>

==Binding Interactions==

<Structure load='4OTI' size='300' frame='true' align='right' caption='4oti, Binding Interactions' scene='Insert optional scene name here' />

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Translocation into the plasma membrane is the ultimate goal of PRK1’s function and can only be achieved after proper activation by phosphorylation of the residues <font color='darkorchid'>Ser 922</font>, in the turn motif of N-lobe, and Thr 780 in the activation loop. The <scene name='48/483882/Phosphorylation/3'>phosphorylation site</scene> of residue <font color='darkorchid'>Ser 922</font> includes a charges pocket of the residues <font color='darkorchid'>Arg 629, Lys 634, and Lys 653</font>, which further prompts the conformational changes in the “hinge point” between the C-terminal and N-terminal. This is required to activate substate and cofactor binding that leads to further conformational changes and eventual translocation and signaling.<ref name="rasmo">DOI: 10.1371/journal.pone.0103638</ref>

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Cofactor binding, which is similar in all Protein Kinases, is located in the <scene name='48/483882/Active_site_tether/1'>active-site tether (AST)</scene>. In this case, the AST is centered around the residue <font color='Blue'>Phe 910</font> that is stacked between <font color='Blue'>Leu 627 and Gly 707</font>, which directs the ATP coordination to the β3 strand in the C-helix. Another important area is the <scene name='48/483882/Clt/1'>C-lobe tether (CLT) site</scene>, which stabilizes the AST site and phosphorylation conformation changes, although it is less understood at this time<ref name="rasmo6">Doi: 10.1073/pnas.0610251104</ref>.

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Most importantly, the AST region of the protein is the target area for protein inhibition in drug treatments. Known inhibitors such as Tofacitinib, lestaurtinib, and Ro-31-8220 interact with the binding site, specifically <font color='Blue'>Phe 910</font>, and disrupt ATP coordination as well as other secondary structure shifts. The MI1 ligand seen in the 4oti green scenes throughout this page is the bound Tofacitinib ligand.

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==Additional Features==

<Structure load='4OTI' size='300' frame='true' align='right' caption='4oti, Additional features' scene='Insert optional scene name here' />

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In individuals with prostate and ovarian cancer, PRK1 is overexpressed in affected cells. Research has shown that higher expression levels correlate with Gleason scores in prostate cancer. Inhibition of PRK1 aids in preventing the proliferation of cancerous cells.<ref name="rasmol" /> <br> PRK1 is capable of moving between the cytoplasm and nucleus. The activity levels of PRK1 can be controlled by a variety of small signaling molecules along with phosphorylation and proteolysis. <br>

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A characteristic feature of PRK1 is a C-terminal regulatory region. This section of the protein regulates enzyme activity and can recruit binding partner <ref name="rasmo6">Doi: 10.1073/pnas.0610251104</ref>.The <font color='red'>C-tail</font> can be found at the base of the C-lobe and encircles the C-lobe. In addition to its main role in the cell, PRK1 also aids in the epigenetic regulation of transcription. A threonine residue, <font color='blue'>Thr 11</font> phosphorylates histone H3 and can enhance transcription of the nearby genes.<ref name="rasmol" /> <br>

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PRK1 is inhibited by the naturally occurring molecule staurosporine. Clinical trials are being ran on several PRK1 inhibitors to observe their medical benefits. Even though PRK1 plays a role in pathways implicated by ovarian and prostate cancer, these inhibitors are being evaluated for treating other diseases. Lestaurtinib (CEP701) is a staurosporine analogue and inhibits several other protein kinases.CEP701 is being evaluated as a potential treatment for myelofibrosis and AML<ref name="rasmo">DOI: 10.1371/journal.pone.0103638</ref>. CEP701 causes a substantial disordering of the C-tail when it binds. Another drug, tofacitinib, has been approved for use as a rheumatoid arthritis treatment. Tofacitinib does not show the same displacement when it binds, but does make van der Waals <scene name='48/483882/Phe910/3'>interactions with the side chain of </scene><font color='teal'>Phe 910</font> . Instead, it results in a clashing with the sidechain of the G-loop residue <scene name='48/483882/Phe632/2'>Phe632</scene> and causes it to position away from the ATP binding site.

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==Quiz Question 1==

<Structure load='4OTI' size='300' frame='true' align='right' caption='Quiz Question 1' scene='Insert optional scene name here' />

4oti is a member of a family of Protein Kinase C related kinases, along with <scene name='48/483882/4otg/1'>4otg</scene>, <scene name='48/483882/4oth/1'>4oth</scene>, and <scene name='48/483882/4otd/1'>4otd</scene>.

Two inhibitors have been proposed for inhibiting PRK1s, Tofactenib:

[[Image:Tofactin.png]]

And Lestaurtinib:

[[Image:Larin.png]]

A) Which inhibitor is most likely to be successful on 4oti? Why? What type of inhibitor is it?

Consider the active site of <scene name='48/483882/4oti_pocket/1'>4oti</scene> and <scene name='48/483882/4oth/2'>4oth</scene>. Note the conservation of the <font color='crimson'>Glu702</font> and <font color='yellowgreen'>Ser704</font> residues, and their positions compared to the <font color='blue'>beta sheets</font>. Compare <scene name='48/483882/4oth_lig/1'>4oth's ligand</scene> to <scene name='48/483882/4oth_lig/2'>4oti's</scene>, and notice that they both hydrogen bond to <font color='crimson'>Glu702</font> and <font color='yellowgreen'>Ser704</font>.

B) What does this tell you about the nature of the active site for <scene name='48/483882/Mi1_quiz/1'>the ligand</scene>, <font color='blueviolet'>MI1</font>, in 4oti compared to 4oth?

==Quiz Question 2==

<Structure load='4oti' size='300' frame='true' align='right' caption='Quiz Question 2' scene='Insert optional scene name here' />

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<scene name='48/483882/Quiz/1'>Of the labeled amino acids, which is most likely to play a role in ligand binding? </scene><br>

a. Phe910 <br>

b. Pro 820<br>

c. Arg 660<br>

d. Both A and B <br>

e. A, B, and C<br>

==See Also==

*[[Protein_kinase_C]]

*[[Androgen_receptor]]

*[[Histone]]

*[[Histone_deacetylase]]

*[[4otd]]

*[[4oth]]

*[[4otg]]

==Credits==

Introduction - Md Shafiul Hossain

Overall Structure - Kevin Purcell & John MacMunn

Binding Interactions - Emily Hutchinson & Emily Friis

Additional Features - Hieu La

Quiz Question 1 - Md Shafiul Hossain, Kevin Purcell & John MacMunn , Emily Hutchinson & Emily Friis, Hieu La

Quiz Question 2 - Md Shafiul Hossain, Kevin Purcell & John MacMunn , Emily Hutchinson & Emily Friis, Hieu La

==References==

<references/>