Synthesis and calpain inhibitory activity of peptidomimetic compounds with constrained amino acids at the P2 position

The effect of incorporating α,α′-diethylglycine and α-aminocyclopentane carboxylic acid at the P₂ position of inhibitors on μ-calpain inhibition was studied. Compound 3 with α,α′-diethylglycine was over 20-fold more potent than 2 with α-aminocyclopentane carboxylic acid. Additionally, 3 was over 35-fold selective for μ-calpain compared to cathepsin B, while 2 was 3-fold selective for cathepsin B compared to μ-calpain. Thus, the conformation induced by the P₂ residue influenced the activities of the compounds versus the closely related cysteine proteases, and suggests an approach to the discovery of selective μ-calpain inhibitors.     

A study of the interactions between an IgG-binding domain based on the B domain of staphylococcal protein a and rabbit IgG

The nonantigenic interaction between a recombinant immunoglobulin G (IgG)-binding protein based on the B domain of Protein A fromStaphylococcus aureus (termed SpA¹) and the Fc fragment of rabbit IgG has been investigated. The contribution to binding of four putative hydrogen bond contacts between SpA¹ and IgG-Fc were examined by the individual substitution of the residues in SpA¹ involved in these interactions by others unable to form hydrogen bonds. It was found that the most important of the hydrogen bonds involved Tyr 18 which, when replaced by Phe, resulted in a twofold decrease in IgG-binding affinity. The residues of SpA¹ proposed to make close, mainly hydrophobic, contacts with Fc were replaced by residues with potential electrostatic charge to establish the importance of the hydrophobic interaction in the complex. The IgG-binding affinities of the mutant proteins were compared to the wild-type protein by a competitive enzyme-linked immunosorbant assay. The replacement of individual hydrophobic residues by His generated a number of novel IgG-binding proteins with reduced binding affinity at pH 5.0 but which maintained strong binding affinities at pH 8.0. The elution profile of human IgG₁-Fc (Fc fragment of human IgG₁) from a column made from an immobilized two-domain mutant protein shows that the complex dissociates at a higher pH relative to that of the non-mutated protein thus offering favorable elution characteristics.     

N-terminus of M2 protein could induce antibodies with inhibitory activity against influenza virus replication

New influenza vaccines have been designed based on the fact that the extracellular domain of M2 protein (M2e) is nearly invariant in all influenza A strains. To clarify which exact region of M2e could induce antibodies with inhibitory activities against influenza virus replication, four overlapping peptides covering M2e were synthesized and then coupled to the carrier protein bovine serum albumin through the cysteine of the peptides. After a vaccination course, all these four peptide vaccines could induce high levels of rabbit antibodies with predefined peptide specificity (antibody dilution: 1:6400-1:25600). Besides, the anti-N-terminal antibodies (AS2) reacted strongly with M2e, and reacted weakly with the middle part and C-terminus of M2e. The MDCK assay for cytopathic effect proved that antibodies recognizing the N-terminus of M2e could obviously inhibit replication of influenza A virus (A/wuhan/359/95) and influenza B virus (B/wuhan/321/99) in vitro in a dose-dependent manner, while antibodies recognizing the middle part and the C-terminus of M2e did not show such significant inhibitory activities. Sequence analysis indicates that the first nine N-terminal amino acid residues of M2e are extremely conservative. Just this region containing the first nine amino acid residues could induce antibodies with inhibitory activity against influenza A and influenza B virus replication, suggesting that the N-terminus of M2e may contain an epitope that could induce inhibitory antibodies against influenza virus replication in vitro.     

The role of the L2 loop in the regulation and maintaining the proteolytic activity of HtrA (DegP) protein from Escherichia coli

The aim of this study was to characterize the role of particular elements of the regulatory loop L2 in the activation process and maintaining the proteolytic activity of HtrA (DegP) from Escherichia coli. We measured the effects of various mutations introduced to the L2 loop’s region (residues 228-238) on the stability of HtrA molecule and its proteolytic activity. We demonstrated that most mutations affected the activity of HtrA. In the case of the following substitutions: L229N, N235I, I238N, the proteolytic activity was undetectable. Thus, the majority of interactions mediated by the studied amino-acid residues seem to play important role in maintaining the active conformation. Formation of contacts between the apical parts (residues 231-234) of the L2 loops within the HtrA trimer, in particular the residues D232, was shown to play a crucial role in the activation process of HtrA. Stabilization of these intermolecular interactions by substitution of D232 with valine caused a stimulation of proteolytic activity whereas deletion of this region abolished the activity. Since the pathogenic E. coli strains require active HtrA for virulence, the apical part of L2 is of particular interest in terms of structure-based drug design for treatment E. coli infections.     

A double WAP domain (DWD)-containing protein with proteinase inhibitory activity in Chinese white shrimp, Fenneropenaeus chinensis

The whey major component, whey acidic protein (WAP), has one or more WAP domains characterized by a four-disulfide core (4-DSC) structure. These kinds of proteins are involved in multiple functions, including proteinase inhibitor activity, antimicrobial activity, ATPase inhibitor activity, and regulatory function in cell proliferation. Recent research indicates that WAP domain-containing proteins play an important role in the innate immunity of crustaceans. In this study, a novel double WAP domain (DWD)-containing protein named Fc-DWD was found for the first time in Chinese white shrimp, Fenneropenaeus chinensis. The open reading frame of Fc-DWD encodes a protein of 117 amino acids, including a signal peptide of 16 amino acids and two WAP domains. The predicted molecular mass of the mature protein is 12.78 kDa with an estimated pI of 8.49. The first WAP domain, named WAP 1, composed of 49 amino acids locates in the amino-terminal of Fc-DWD, and the second WAP domain, named WAP 2, composed of 45 amino acids locates in the carboxy-terminal. Fc-DWD mRNA was upregulated in hemocytes, hepatopancreas, gills, and stomach of bacteria- and virus-challenged shrimp. Results of the binding assay showed that rFc-DWD could bind to both Gram-negative bacteria and Gram-positive bacteria. rWAP 1 could only bind to Gram-positive bacteria, but rWAP 2 could bind to both Gram-negative and positive bacteria. Moreover, rFc-DWD exhibited proteinase inhibitory activity against the secretory proteinase(s) from Bacillus subtilis and Pseudomonas aeruginosa. All of these findings suggest that Fc-DWD may play an important role in enabling the host defense to execute its proteinase inhibitory activity against pathogens.