TOR PROTEINS

The TOR proteins were first identified in Saccharomyces cerevisiae, where rapamycin is growth-inhibitory.The rapamycin/FKBP12 complex binds directly to TOR, and the TOR mutations that confer rapamycin resistance in situ result in a loss of rapamycin/FKBP12 binding . The role of TOR as the rapamycin target responsible for inhibition of p70 S6 kinase .Rapamycin is an immunosurpressive whose cellular receptor is the cytosolic 12-kDa FK506-binding protein (FKBP12). Rapamycin binds to FKBP12  are immunosurpressive through inhibition of T-cell proliferation.  

PROTEINS SENSITIVE TO RAPAMYCIN-

1.The proteins eIF-4E BP1 and p70 S6 kinase each undergo an insulin/mitogen-stimulated phosphorylation in situ that is partially inhibited by rapamycin. mTOR mutants also protect eIF-4E BP1 against rapamycin-induced dephosphorylation, and for both p70 S6 kinase and eIF-4E BP1, such protection requires that the rapamycin-resistant mTOR variant retains an active catalytic domain. In contrast, mutants of p70 S6 kinase rendered intrinsically resistant to inhibition by rapamycin in situ are not able to protect coexpressed eIF-4E BP1 from rapamycin-induced dephosphorylation. We conclude that mTOR is an upstream regulator of eIF-4E BP1 as well as the p70 S6 kinase; moreover, these two mTOR targets are regulated in a parallel rather than sequential manner.

2.PHAS-1 is another rapamycin-sensitive protein; this 12-kDa polypeptide binds to the 7-methylguanosine cap-binding protein, eIF-4E, and prevents eIF-4E binding to p220/eIF-4G. 

PART -C QUESTION 
Insulin and other growth factors stimulates a pathway involving protein kinase m-TOR which in its turn augments protein synthesis .m-TOR  essentially modifies proteins which in their unmodified form act as inhibitors of protein synthesis .The following proteins are possible candidates -
A.eEF-1
B.eIF-4E-BP1
C.eIF-4E
D.PHAS-1
Which of the following sets are correct 
a. A & B                        c.A A& C 
b.B & D                         d.B & C 

ANSWER - b (B& D)

Thank you for visiting my  blog.  Share your comments on this

article.  Subscribe and follow me in Google + to get notified with new articles.

NON STANDARD AMINO ACIDS

Apart from the 20 standard amino acids, all the rest amino acids are called as ‘non-standard’ amino acids. These include both proteinogenic as well as non-proteinogenic amino acids.  

Amino acid derivatives as proteins (Proteinogenic)

• 4-hydroxyproline = found in plant cell wall proteins, also  in collagen.
• 5-hydroxylysine= found in collagen
• 6-N-methyllysine= found in myosin, a muscle protein
• γ-carboxyglutamate = found in prothrombin  and certain other proteins that bind Ca₂⁺ ions.
• Desmosine= found in fibrous protein elastin
• N-Formylmethionine= It is initially the N-terminal residue of all prokaryotic proteins.

 D-amino acid residues form polypeptides that are generally found to constitute bacterial cell walls. Apart from this, certain bacterially produced peptide antibiotics also contain D amino acids like valinomycin, gramicidin A and actinomycin D. 

Other amino acids (Non-proteinogenic) 

Besides their role in protein synthesis, amino acids also serve various other important functions.

• Some amino acids act as neurotransmitters like γ-aminobutyric acid (GABA) that’s formed as a result of glutamate decarboxylation and dopamine that’s a tyrosine derivative.
•          Histamine which is formed as a result of decarboxylation of histidine is a local mediator of allergic reactions
•  Tyrosine derivative thyroxine is a thyroid hormone.
• Ornithine and citrulline are intermediates in the biosynthesis of arginine and urea cycle.
•  Homocysteine is an intermediate in amino acid metabolism.
• S-adenosylmethionine is a biological methylating reagent.
• Azaserine is a medically useful antibiotic.

Thank you for visiting my  blog.  Share your comments on this

article.  Subscribe and follow me in Google + to get notified with new articles.