Conformational Preferences of Linear β-Defensins Are Revealed by Ion Mobility-Mass Spectrometry

Abstract

In recent times there has been an enormous rise in resistance to synthetic antibiotics as well as an increase in the virulence of bacteria, the so-called "superbugs". This problem has catalyzed a search for novel molecules to fight bacteria, which in turn relies on a better understanding of the molecular basis of the immune response. Beta-defensins are a class of small, cationic, cysteine-rich antimicrobial peptides expressed by humans and other animals to act against incoming pathogens. As well as their antimicrobial properties, beta-defensins also act as chemokines, recruiting cells to the sites of infection. Here the relationship between the tertiary structures of beta-defensin analogs and their chemotactic activities has been investigated using ion mobility-mass spectrometry (IM-MS) and biochemical assays. A panel of derivatives of the murine beta-defensin Defb14 has been formed and the ability of these peptides to chemoattract the receptor CCR6 has been assessed in vitro. The derivatives can be divided into two groups, those with chemotactic activity equal to that of the unmodified parent peptide, and those whose chemotactic activity has been lost upon modification. Analysis by ion mobility-mass spectrometry reveals the conformational preferences of these peptides upon ionization from different solvents. Under denaturing conditions, the chemotactic peptides adopt more compact conformations in the gas-phase at higher charge states than those which are inactive. While the conditions of these experiments are not akin to the environment around the receptor in vivo, this technique provides an in vacuo method for distinguishing between the different chemotactic activities of beta-defensin derivatives.

Will new generations of modified antimicrobial peptides improve their potential as pharmaceuticals?

“…Free cysteines in the C-terminus are important for the bactericidal effect. Also, congeners of linear β-defensins have differing chemotactic activities related to their conformational status [83]. …”

Interaction of cations with 2′‐deoxythymidine nucleoside and analysis of the nature and strength of cation bonds

“…They also used DFT (B3LYP) to investigate the thermodynamics and kinetics of the glycosidic bond cleavage reaction in the model nucleoside forms of guanine and its major oxidation product, 8‐oxoguanine. Their results provided a greater understanding of the relative effects of the nucleophile, the damage to the nucleobase, and the nucleobase orientation with respect to the sugar moiety on the deglycosylation pathway, which provide qualitative explanations for relative base excision rates observed in some biological systems …”

Gas‐phase conformations of capistruin – comparison of lasso, branched‐cyclic and linear topologies

“…A complementary approach to fragmentation experiments is to use ion mobility spectrometry coupled to mass spectrometry (IMS‐MS) in order to obtain information on the global shape of the investigated molecules. IMS has indeed shown its potential for the structural characterization of biomolecules or biomolecular complexes, including molecules with topological constraints, such as peptides containing disulfide bonds, or branched polymers . It is based on the measurement of the drift time of ions in a buffer gas, under the influence of a weak electric field.…”