The antimicrobial peptide, lactoferricin, is generated upon the gastric pepsin cleavage of lactoferrin and has many basic and hydrophobic amino acid residues essential for its biological activity. To investigate the structure‐antimicrobial activity relationships, the basic amino acid‐rich region of bovine lactoferricin (BLFC), RRWQWRMKKLG, was selected. Using chemically synthesized BLFC and its substituted peptides, the antimicrobial activities of the peptides were tested by determining the minimal inhibitory concentration (MIC) of Escherichia coli and Bacillus subtilis and the disruption of the outer cell membrane of E. coli, and the peptide's toxicities were assayed by hemolysis. The short peptide (B3) composed of only 11 residues had similar antimicrobial activities while losing most of the hemolytic activities as compared with the 25 residue‐long ones (B1 and B2). The short peptides (B3, B5 and B7) with double arginines at the N‐termini had more potent antimicrobial activity than those (B4 and B6) with lysine. However, no antimicrobial and hemolytic activities were found in B8, in which all basic amino acids were substituted with glutamic acid, and in B9, in which all hydrophobic amino acids were substituted with alanine. The circular dichroism (CD) spectra of the short peptides in 30 MM SDS were correlated with their antimicrobial activities. These results suggested that the 11‐residue peptide of BLFC is involved in the interaction with bacterial phospholipid membranes and plays an important role in antimicrobial activity with little or no hemolytic activity. © Munksgaard 1996.

A 20-residue hybrid peptide (CA(1-8)-MA(1-12): KWKLFKKIGIGKFLHSAKKF-NH(2)) incorporating 1-8 residues of cecropin A (CA) and 1-12 residues of magainin 2 (MA) has potent antibiotic activity without hemolytic activity. In order to investigate the effects of the flexible hinge sequence, Gly-Ile-Gly of CA(1-8)-MA(1-12) (CA-MA) on antibiotic activity, CA-MA and its three analogues, CA-MA1, CA-MA2 and CA-MA3 were synthesized. The Gly-Ile-Gly sequence of CA-MA was deleted in CA-MA1 and replaced with Pro and Gly-Pro-Gly in CA-MA2 and CA-MA3, respectively. CA-MA1 and CA-MA3 caused a significant decrease in the bactericidal rate against Escherichia coli and Bacillus subtilis and the tumoricidal activity against four different tumor cells, and the PC/PS (4:1, w/w) vesicle-aggregating and disrupting activities. However, CA-MA2 showed a similar bactericidal rate and antitumor, vesicle-aggregating and disrupting activities, as compared with CA-MA. These results suggested that the flexibility or beta-turn induced by Gly-Ile-Gly or Pro in the central part of CA-MA may be important in the electrostatic interaction of the cationic short alpha-helical region in the N-terminus with the cell membrane surface and the hydrophobic interaction of amphipathic alpha-helical region in the C-terminus with the hydrophobic acyl chains in the cell membrane. CA-MA3 exhibited lower activity in antibacterial, antitumor, and vesicle-aggregating and disrupting activities than CA-MA and CA-MA2. This result suggested that the excessive beta-turn structure by Gly-Pro-Gly in CA-MA3 seems to interrupt the ion channel/pore formation on the lipid bilayer. It was concluded that the appropriate flexibility or beta-turn structure provided by the central hinge is responsible for the effective antibiotic activity of the antimicrobial peptides with the helix-hinge-helix structure.

The hybrid peptide (CA‐ME) derived from cecropin A(1–8) and melittin(1–12) has potent antibacterial and antimalarial activities. Because the N‐terminal sequence 1–12 of magainin 2 is similar to melittin(1–12), CA‐MA with CA(1–8) and MA(1–12) and their analogues were designed and synthesized. Antitumor activities of these peptides were evaluated using three small cell lung cancer cell lines. Greater antitumor activity was observed when the residues 16, 18 and 19 of the peptide were hydrophobic (Leu or Val), basic (Lys) and basic (Lys), respectively. The IC50 values of the peptides with the residues were 2 to 4 μm. Residue 12 was related to hemolytic activity rather than antitumor activity. Increase in amphipathicity of P4 enhanced hemolytic activity without significant change in antitumor activity. The α‐helicity of the peptides in a 30 mm sodium dodecyl sulfate solution was more closely correlated to hemolytic activity than antitumor activity.

In order to elucidate the structure-antibiotic activity relationships of the peptides, the three-dimensional structures of two hybrid peptides, CA(1-8) - MA(1-12) and CA(1-8) - ME(1-12) in trifluoroethanol-containing aqueous solution were investigated by NMR spectroscopy. Both CA(1-8) - MA(1-12) and CA(1-8) - ME(1-12) have strong antibacterial activity but only CA(1-8) - ME(1-12) has hemolytic activity against human erythrocytes. CA(1-8) - MA(1-12) has a hydrophobic 310-helix of only two turns combined with one short helix in the N-terminus with a flexible hinge section in between. CA(1-8) - MA(1-12) has a severely bent structure in the middle of the peptide. These structural features as well as the low hydrophobicity of CA(1-8) - MA(1-12) seem to be crucial for the selective lysis against the membrane of prokaryotic cells. CA(1-8) - ME(1-12) has an alpha-helical structure of about three turns in the melittin domain and a flexible structure with one turn in the cecropin domain connected with a flexible hinge section in between, and these might be the structural features required for membrane disruption against prokaryotic and eukaryotic cells. The central hinge region (Gly9-Ile10-Gly11) in an amphipathic antibacterial peptide is considered to play an important role in providing the conformational flexibility required for ion channel formation of the C-terminal hydrophobic alpha-helix on cell membrane.

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Anti-hepatitis B virus (HBV) surface-antigen immunoglobulins prepared from human sera are clinical reagents which have been approved for prophylactic treatment in HBV-exposed persons. The passive immunoprophylaxis with immunoglobulins is meant to cross-link viral particles, which are then further cleared by the host's own immune system. While antibodies specific for both anti-S-and anti-preS proteins have been proved to serve as effective anti-viral agents, so far the fine antigen specificity of clinical immunoglobulin preparations has not been determined. Using recombinant proteins covering the hepatitis B surface antigen, in the present study, the specificity of a commercially available immunoglobulin preparation was determined and immunodominant epitopes were mapped. Here, it is shown that the major reactivity of anti-HBV immunoglobulins is directed against the S-protein, and that no reactivity to the preS2 but a weak binding activity to the preS1 region was detectable. The antigen reactivity within the preS1 region was biased to the C-terminal region, which indicates the presence of a putative B-cell epitope. The evaluation of the antigen specificity and determination of novel protective epitopes will provide valuable information for the further development and improvement of prophylactic HBV immunoglobulins.

The stress response alters behavior, autonomic function, and secretion of multiple hormones, including corticotropin-releasing factor, adrenocorticotropin hormone, and cortisol, through the hypothalamic-pituitary-adrenal axis. Constitutive stress responses lead to a number of psychiatric disorders, including depression, posttraumatic stress disorder, Alzheimer's disease (AD), and other anxiety disorders through increased stress hormones and other unknown factors. Here, we performed a proteomic analysis of rat brain exposed to restraint stress compared with a nonstress group by using 2D-DIGE and MALDI-TOF analysis. Several proteins were identified by peptide mass fingerprint (PMF), including down-regulated hippocampal cholinergic neurostimulating peptide precursor protein (HCNP-pp). The current study demonstrates that HCNP-pp mRNA and protein expression are decreased in rat hippocampus after stress exposure. The level of HCNP-pp in H19-7, a rat hippocampal cell line, significantly decreases with dexamethasone treatment, a synthetic glucocorticoid. Thus, this finding suggests that HCNP-pp expression may decrease in response to stress exposure. Decreased HCNP-pp from stress exposure may result in lower levels of HCNP that might contribute to a loss of acetylcholine production.