Effect of N- and C-Terminal Amino Acids on the Interfacial Binding Properties of Phospholipase D from Vibrio parahaemolyticus

The effects of N-terminal (1–34 amino acids) and C-terminal (434–487 amino acids) amino acid sequences on the interfacial binding properties of Phospholipase D from Vibrio parahaemolyticus (VpPLD) were characterized by using monomolecular film technology. Online tools allowed the prediction of the secondary structure of the target N- and C-terminal VpPLD sequences. Various truncated forms of VpPLD with different N- or C-terminal deletions were designed, based on their secondary structure, and their membrane binding properties were examined. The analysis of the maximum insertion pressure (MIP) and synergy factor “a” indicated that the loop structure (1–25 amino acids) in the N-terminal segment of VpPLD had a positive effect on the binding of VpPLD to phospholipid monolayers, especially to 1,2-dimyristoyl-sn-glycero-3-phosphoserine and 1,2-dimyristoyl-sn-glycero-3-phosphocholine. The deletion affecting the N-terminus loop structure caused a significant decrease of the MIP and synergy factor a of the protein for these phospholipid monolayers. Conversely, the deletion of the helix structure (26–34 amino acids) basically had no influence on the binding of VpPLD to phospholipid monolayers. The deletion of the C-terminal amino acids 434–487 did not significantly change the binding selectivity of VpPLD for the various phospholipid monolayer tested here. However, a significant increase of the MIP value for all the phospholipid monolayers strongly indicated that the three-strand segment (434–469 amino acids) had a great negative effect on the interfacial binding to these phospholipid monolayers. The deletion of this peptide caused a significantly greater insertion of the protein into the phospholipid monolayers examined. The present study provides detailed information on the effect of the N- and C-terminal segments of VpPLD on the interfacial binding properties of the enzyme and improves our understanding of the interactions between this enzyme and cell membranes.

Psychrometric Wet Elements as a Basis For Precise Physico-Chemical Measurements

Under appropriate conditions, psychrometric wet elements of simple design can he highly reproducible in behavior. A temperature depression of 10 K can be reproducible from element to element within 2 mK. The properties of a wet element can be determined very accurately by direct comparisons with other wet elements in a common airstream. Comparisons with one specially developed type show the effects of practical water-retaining coverings. Comparisons with another type, which simulates the fully calculable flat-plate system, then give the behavior in absolute terms. A cotton-yarn covering increases the psychrometer coefficient A by only 0.2 percent. The departure of the flow around a cylinder from laminar boundary-layer flow increases it by 0.7 percent. The background and theory are outlined. The detailed behavior of cotton-yarn covered cylinders is deduced from element comparisons; and their absolute value of A obtained as a function of diameter, airspeed, and the temperature, pressure and water content of the airstream. The dependence of A on these parameters is essentially simple. The work leads to a large increase in the accuracy of water vapor measurements and to new methods of measuring some other physico-chemical quantities.