Occurrence and evolutionary conservation analysis of α-helical cationic amphiphilic segments in the human proteome

Positively charged residues play a significant role in enhancing the antibacterial activity of calcitermin

A systematic study on the human antimicrobial peptide calcitermin (VAIALKAAHYHTHKE) and its carefully designed derivatives was undertaken to verify the impact of divalent copper and zinc ions on the stability, coordination and antimicrobial activity of the formed complexes. In this work we investigate the calcitermin mutants where the alanine in position 7 and 8 is substituted with an arginine residue, with the aim of enhancing the antibacterial activity. Additionally, the analogue where alanine in position 7 is replaced with a histidine is considered, to obtain a chelating sequence with four histidines in alternate position; the aim of this change was to increase the cationic properties of the peptide under acidic conditions and possibly enhance its binding ability towards the metal ions. Through a comprehensive analytical approach involving potentiometric titrations, mass spectrometry, UV-Vis spectrophotometry, NMR and circular dichroism, we delved into the formation equilibria and coordination chemistry of the formed copper(II) and zinc(II) complexes. Antimicrobial assays are also performed to assess the bioactivity of the compounds against a broad spectrum of microorganisms, revealing the pivotal role of positively charged residues in enhancing the antibacterial activity of calcitermin. The obtained results serve as an important stepping stone towards the development of novel metal-based antimicrobial agents.

Intragenic antimicrobial peptide Hs02 toxicity against leukemia cell lines is associated with increased expression of select pyroptotic components

The anticancer potential of some antimicrobial peptides has been reported. Hs02 is a recently characterized Intragenic Antimicrobial Peptide (IAP), which was able to exhibit potent antimicrobial and anti-inflammatory action. In this study, we evaluate for the first time the antineoplastic potential of the Hs02 IAP using cell lines representing the main types of leukemia as cancer models. Interestingly, this peptide decreased the viability of several leukemic cell lines, without compromising the viability of PBMCs in the same concentration. In the HL-60 line, treatment with Hs02 controlled cell division, leading to cell arrest in the G1 phase of the cell cycle. More importantly, HL-60 cells treated with Hs02 undergo cell death, with the formation of pores in the plasma membrane and the release of LDH. Accordingly, Hs02 treatment stimulated the expression of components involved in pyroptosis, such as NLRP1, CASP-1, GSDME, and IL-1β. Taken together, our data characterize the antineoplastic potential of Hs02 and open an opportunity for both evaluating the peptide's antineoplastic potential in other cancer models and using this molecule as a template for new peptides with therapeutic potential against cancer.

Sequence-dependent and -independent information in a combined random energy model for protein folding and coding

Random energy models (REMs) provide a simple description of the energy landscapes that guide protein folding and evolution. The requirement of a large energy gap between the native structure and unfolded conformations, considered necessary for cooperative, protein-like, folding behavior, indicates that proteins differ markedly from random heteropolymers. It has been suggested, therefore, that natural selection might have acted to choose nonrandom amino acid sequences satisfying this particular condition, implying that a large fraction of possible, unselected random sequences, would not fold to any structure. From an informational perspective, however, this scenario could indicate that protein structures, regarded as messages to be transmitted through a communication channel, would not be efficiently encoded in amino acid sequences, regarded as the communication channel for this transmission, since a large fraction of possible channel states would not be used. Here, we use a combined REM for conformations and sequences, with previously estimated parameters for natural proteins, to explore an alternative possibility in which the appropriate shape of the landscape results mainly from the deviation from randomness of possible native structures instead of sequences. We observe that this situation emerges naturally if the distribution of conformational energies happens to arise from two independent contributions corresponding to sequence-dependent and -independent terms. This construction is consistent with the hypothesis of a protein burial folding code, with native structures being determined by a modest amount of sequence-dependent atomic burial information with sequence-independent constraints imposed by unspecific hydrogen bond formation. More generally, an appropriate combination of sequence-dependent and -independent information accommodates the possibility of an efficient structural encoding with the main physical requirement for folding, providing possible insight not only on the folding process but also on several aspects sequence evolution such as neutral networks, conformational coverage, and de novo gene emergence.