Analysis Of Trypsin-1

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The assigned sequence was most closely matched via the BLAST algorithm with the retrieved sequence of Trypsin-1, accession no P07477.7 [1] (Appendix 1).
Trypsin-1 is a 247 amino acid long protein [2] (Appendix 3) of the serine protease family, with a molecular mass of 26,558 Daltons [3] (Appendix 2). It is globular in shape and contains two regions of α-helices and multiple regions of β-sheets, as seen in Figure 1[4]. It contains disulphide bonds at residue positions 30/160, 48/64, 139/206, 171/185 and 196/220. The tyrosine-154 undergoes sulphation as a post translational modification. There are 22 negatively charged and 20 positively charged residues which contribute to a theoretical pI of 6.02 [2] (Appendix 3).
Trypsin-1 is a zymogen. Residues
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This increased electronegativity allows the histidine to attract the hydrogen in the serine’s –OH group. This boosts the nucleophilic behaviour of the serine and allows it to attack and facilitate the cleavage of the substrate. A calcium cofactor for this reaction is bound by residues 75, 77, 80 and 85 [3] (Appendix 2).
Trypsin-1 is created in the pancreas and excreted extracellularly [3] (Appendix 2). It then enters the small intestine during digestion, where it facilitates the breakdown of proteins for their subsequent absorption into the blood stream [6]. Reside R116 forms an autocatalytic site for degradation by another activated trypsin [9]. This is thought to prevent degradation of pancreas by elevated trypsin activity.
Figure 1: Structure of Trypsin-1. Retrieved from the Protein Data Bank.
Figure 1: Structure of the catalytic triad. Residues D63, H107 and S200 as shown. Arrows represent the flow of charge that increases the serine’s nucleophile behaviour.
James Gatenby SID:310255511
2. Examination of Sequence
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These include H63K, D107Q and S200T. All three of these changes incorporate amino acids that are slightly larger. It is possible that this will create steric hindrance that will prevent the substrate from binding to the active site. D107Q changes the residue from negatively charged to polar, which may deleteriously decrease the electronegativity of the neighbouring residue (H63K). This neighbouring residue has had general charge conserved as positive, however the pKa of lysine is vastly different from histidine. While histidine’s pKa of 6.04 allows it to act as a nucleophile part of the time, lysine’s pKa of 10.07 means it is usually positively charged and unable to do the same. S200T does not change the functional group of the residue, so it may still be able to act as a nucleophile. However, it may be limited without the charge carrying role of histidine. For all these reasons, it is probable that the enzyme has decreased or no function as a protease. In an animal, this may result in a decreased ability to digest and absorb

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