Elastase domains

FlC. 64. The tightly associated domains (one shown light and the other dark) of elastase. Figures 64 through 66 use a space-filling representation with a sphere around each a-carbon position they were photographed from Richard Feldmann s molecular graphics display at the National Institutes of Health. 

Fig. 68. Schematic backbone drawing of the elastase molecule, showing the similar 0 barrel structures of the two domains. The outside surfaces of the 0 barrels are stippled.

The separateness of two domains within a subunit varies all the way from independent globular domains joined only by a flexible length of polypeptide chain, to domains with tight and extensive contact and a smooth globular surface for the outside of the entire subunit, as in the proteolytic enzyme elastase (fig. 4.20). An intermediate level of domain separateness, characterized by a definite neck or cleft between the domains, is found in phosphoglycerate kinase (fig. 4.21). 

We were also able to use FAB mass spectrometry to determine the amino acid sequence around the active site serine in the acyl transference domain of rabbit mammary fatty acid synthase.6 The synthase was labelled in the acyl transferase domain(s) by the formation of O-ester intermediates after incubation with [" " C]-acetyl- or malonyl-CoA (Fig. 2A). The modified protein was then digested with elastase (Fig. 2B), and radioactive material isolated via successive purification steps on Sephadex G-50 and reverse phase HPLC. The isolated peptides were then sequenced by FAB MS. The data summarized in Table II established the sequences of both the acetyl and malonyl hexapeptides to be N-acyl-Ser-leu-Gly-Glu-Val-Ala. 

Protein-Protein Interaction The Binding of Ovomucoid Third Domain to Elastase. 

Bik inhibits the trypsin serine proteases through binding of either of its two Kunitz domains. Depending on the serine protease and the Kunitz domain involved, dissociation constants (K ) range from 0.03 to 800 pM [6, 28]. Bik fragmentation and glycation also effect strength and specificity of inhibition. For example, trypsin, chymotrypsin, kallikrein, plasmin, elastase, and cathepsin are inhibited at a A) of 0.03-3 pM, whereas Factors IXa, Xa, XIa, and Xlla are less inhibited with a A) of 15-800 pM. Protease inhibition is observed with both Kunitz domains except for Factors IXa and Xa that... 

Trypsin cleaves a peptide bond on the C-terminal side of a basic residue such as arginine (Arg) or lysine (Lys) whereas chymotrypsin cleaves on the C-terminal side of the hydrophobic residues phenylalanine (Phe), tryptophan (Trp) or tyrosine (Tyr). Elastase cleaves on the C-terminal side of small amino acids such as alanine (Ala) and glycine (Gly). A large number of serine PI proteins have been isolated from plants (Table 13.4) and the substrate specificity of the target proteases corresponds with the inhibitory amino acid sequences (P2-P1-PT-P2 ) of the PI proteins. Thus, the double-headed trypsin- and chymotrypsin-inhibitory Bowman-Birk PI protein 1 (BBI-1) from soybean (Glycine BBI-1, Table 13.5G) has a Pl-PT sequence of Lys—Ser at the trypsin inhibitory domain I site and a PI PI sequence of Leu-Ser at the chymotrypsin inhibitory domain II site. 

Baker, B., and Murphy, K. (1997). Dissecting the Energetics of a Protein-protein Interaction The Binding of Ovomucoid Third Domain to Elastase, J. Mol. Biol. 268 557-569. 

Crystal Structure of the Complex of Human Leukocyte Elastase (PMN Elastase) and the Third Domain of the Turkey Ovomucoid Inhibitor. 

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