Allosteric modulation of primary specificity of serine proteinases

Размещено на http://www.Allbest.Ru/

O.O. Bogomolets National Medical University, Ukraine

SI «O.S. Kolomiychenko Institute of Otolarynglology, NAMSU»

Allosteric modulation of primary specificity of serine proteinases

Malezhyk A.O., Student

Voroshylova N.M., C. Biol. Sci., Sen. Lecturer

Obernikhina N.V., C. Chem. Sci., Ass. Prof.

Kyiv, Ukraine

Summary

Keywords: proteolysis, serine proteinases, specificity, allosteric site.

Анотація

Алолостерична модуляція первинної специфічності серинових протеїназ

Селективність дії серинових протеїназ опосередковується високоспецифічним зв'язуванням відповідних частин білкового субстрату. Серед таких білкових мішеней особливе місце займають ділянки функціонально обумовленої взаємодії з активним центром ферменту. Їх різка різниця в спорідненості до ферментів зумовлена синхронною взаємодією зв'язувальних і алостеричних центрів активного центру з адекватними за специфічністю і розміщеними в належній конформації специфічними амінокислотними залишками субстрату. Дана стаття присвячена розгляду прояву алостеричної ерозії первинної специфічності серинових протеїназ. Обговорюються приклади таких ефектів, а також можливості їх застосування.

Ключові слова: протеоліз, серинові протеїнази, специфічність, алостеричний сайт.

Serine proteinases form a large family of enzymes involved in countless physiological and pathophysiological processes. Each of the enzymes performs their functional role due to substrate specificity, i.e. the ability to recognize and interact with a specific bond of the target protein. The simplest serine proteinases are pancreatic enzymes - trypsin, chymotrypsin and elastase (E.C.3.4.21.1,3.4.21.4 and 3.4.21.11, respectively). They are characterized by close values of molecular weights, high degrees of homology of primary sequences and tertiary structures. The kinetic parameters of these enzymes are quite similar, too. The basis for the difference between them is their primary substrate specificity. Trypsin splits specifically the bonds formed by the carboxyl group of positively charged amino acids, chymotrypsin splits on large hydrophobic amino acids, elastase is characterized by hydrolysis of small hydrophobic ones. This is due to differences in the structure of the "hydrophobic pocket" that connects the side chain of the corresponding aminoacids [1]. The chymotrypsin molecule has a recess with dimensions of 12x6.5x4A, which is able to bind large hydrophobic radicals. This allows you to place in it the aromatic residue of Phe, Tyr, Trp, Leu or Ile. In the trypsin molecule at the bottom of a similar pocket instead of Ser189 is Asp189. Its carboxyl group forms an ionic bond with the positively charged amino- or guanidine groups of Lys or Arg. In the case of elastase, the two glycines at positions 216 and 226 are replaced by Val216 and Thr226. This ensures that only small Ala or Val side chains are connected. That's why the primary specificity of the simplest serine proteinases is determined by the parameters of the "hydrophobic pocket". According to the generally accepted Schechter &-Berger nomenclature, it is designated as S1 (Fig. 1).

Fig. 1. The placement of polypeptide chain at the interaction with enzyme by Schechter &-Berger [2]. The arrow indicates the peptide bond that is being cleaved

Similarly, to numerous enzymes, serine proteinases are allosteric ones. Their allosteric site corresponds to S₂ subsite according to Schechter & Berger nomenclature. The interaction of this site with complementary ligand affects the catalytic properties of the enzyme and leads to an increase in its binding and catalytic properties. allosteric erosion serine proteinase conformation amino acid

Synchronous interaction of the binding and allosteric regions of the enzyme with amino acid residues in Pi and P₂' positions of the target bond the highest mutual affinity between enzyme and substrate. The mutual placement of these residues can either be fixed in the optimal canonical conformation, or be in a state of dynamic equilibrium with it [4]. Thus, in most cases of interaction of serine proteinases with reactive centers of protein inhibitors and sites of activative cleavage of pro-forms of various proteins, the P1 position is occupied by an amino acid residue corresponding to the primary specificity of the enzyme. Hydrophobic or positively charged residues are placed in their P2'-positions [5].;

However, such interaction leads to some kind of erosion of the primary specificity of serine proteinases. Thus, the main pancreatic trypsin inhibitor (Lys*- Ala-Arg reactive center) effectively blocks not trypsin only but chymotrypsin, too [6]. In contrast, the a1-proteinase inhibitor (Met*-Ser-Ile reactive center) effectively blocks elastase, trypsin, and chymotrypsin [7]. Affinity sorbents with spatially dispersed hydrophobic ligands (Fig. 2) effectively bind not chymotrypsin-like enzymes only but also trypsin-like ones.

Fig. 2. Affinity ligands with spaced hydrophobic groups [8]

These and similar examples show that with the full participation of the allosteric site in the interaction of serine proteases with complementary structures the substituent in the P1 position does not play a crucial role. This significantly expands the spectrum of the action of corresponding proteinases, providing blockade of the enzyme or its activation cleavage in unexpected areas.

References

1. Fersht, A. Enzyme Structure and Mechanism. 2nd Edition (1984). W.H. Freeman, New York, 475 p.

2. Schechter, I., Berger, A. (1967). On the size of the active site in proteinases. I. Papain. Biochem. Biophys. Res. Communs., 27(2), 157-162.

3. Dobo, J., Gettins, P. (2004). a1-proteinase inhibitor forms initial non-covalent and final covalent complexes with elastase analogously to other serpin-proteinase pairs. J.Biol.Chem. 279(10), 9264-9269.

4. Verevka, S.V. (20220. Allosteric site of serine proteinases: location, functional role and manifestations in vitro. Grail of Science. 12-13, 188-197.

5. Laskowski, M., Empie, M., Kato, I., et al. (1981). Correlation of amino acid sequence witj inhibitor activity and sprcificity of protein inhibitors of serine proteinases. Coll.Les.Biol.Chem. 9(32), 136-152.

6. Blow, D., Wright, C. (1997). A model for the association of bovine pancreatic trypsin inhibitor with chymotrypsin and trypsin. J. Mol. Biol. 69(1), 137-44.

7. Kaslik, G., Kardos, J., Szabo, E., et al. (1997). Effects of serpin binding of the target proteinase: global stabilization, localized increased structural flexibility, and conserved hydrogen bonding at the active site. Biochem. 36(18), 5455-5464,

8. Kolodzeiskaya, M., Verevka, S. (1990). Comparative study of the inherent properties of serine proteases of lower and higher vertebrates. Ukr. Biochem. Journ. 62(6), 31-37 (in Russian).

Размещено на Allbest.Ru