Charged N-terminus of Influenza Fusion Peptide Facilitates Membrane Fusion.

Cleavage of hemagglutinin precursor (HA0) by cellular proteases results in the formation of two subunits, HA1 and HA2. The N-terminal fragment of HA2, named a fusion peptide (HAfp), possess a charged, amine N-terminus. It has been shown that the N-terminus of HAfp stabilizes the structure of a helical hairpin observed for a 23-amino acid long peptide (HAfp1-23), whose larger activity than HAfp1-20 has been demonstrated recently. In this paper, we analyze the effect of N-terminal charge on peptide-mediated fusion efficiency and conformation changes at the membrane interface by comparison with the corresponding N-acetylated peptides of 20- and 23-amino acid lengths. We found that higher fusogenic activities of peptides with unmodified amino termini correlates with their ability to form helical hairpin structures oriented perpendicularly to the membrane plane. Molecular dynamics simulations showed that acetylated peptides adopt open and surface-bound conformation more often, which induced less disorder of the phospholipid chains, as compared to species with unmodified amino termini.

Three conserved C-terminal residues of influenza fusion peptide alter its behavior at the membrane interface.

The N-terminal fragment of the viral hemagglutinin HA2 subunit is termed a fusion peptide (HAfp). The 23-amino acid peptide (HAfp1-23) contains three C-terminal W21-Y22-G23 residues which are highly conserved among serotypes of influenza A and has been shown to form a tight helical hairpin very distinct from the boomerang structure of HAfp1-20. We studied the effect of peptide length on fusion properties, structural dynamics, and binding to the membrane interface. We developed a novel fusion visualization assay based on FLIM microscopy on giant unilamellar vesicles (GUV). By means of molecular dynamics simulations and spectroscopic measurements, we show that the presence of the three C-terminal W21-Y22-G23 residues promotes the hairpin formation, which orients perpendicularly to the membrane plane and induces more disorder in the surrounding lipids than the less structured HAfp1-20. Moreover, we report cholesterol-enriched domain formation induced exclusively by the longer fusion peptide.

Intrinsic Frequency Analysis and Fast Algorithms.

Intrinsic Frequency (IF) has recently been introduced as an ample signal processing method for analyzing carotid and aortic pulse pressure tracings. The IF method has also been introduced as an effective approach for the analysis of cardiovascular system dynamics. The physiological significance, convergence and accuracy of the IF algorithm has been established in prior works. In this paper, we show that the IF method could be derived by appropriate mathematical approximations from the Navier-Stokes and elasticity equations. We further introduce a fast algorithm for the IF method based on the mathematical analysis of this method. In particular, we demonstrate that the IF algorithm can be made faster, by a factor or more than 100 times, using a proper set of initial guesses based on the topology of the problem, fast analytical solution at each point iteration, and substituting the brute force algorithm with a pattern search method. Statistically, we observe that the algorithm presented in this article complies well with its brute-force counterpart. Furthermore, we will show that on a real dataset, the fast IF method can draw correlations between the extracted intrinsic frequency features and the infusion of certain drugs.