Gentle protein ionization assisted by high -velocity gas flow and thermal formation of homochiral serine clusters

Pengxiang Yang, Purdue University

Abstract

Soft ionization is achieved using a conventional ESI source by adding a high-velocity gas flow provided by an air amplifier to improve desolvation. Comparisons are made between the ESI spectra of model proteins over a range of pH values with and without using the air amplifier to achieve high-velocity gas flow. Significant changes in the charge state distribution are observed with a shift to lower charge state at high velocity flow. Data suggest retention of native or native-like protein conformations and more complete desolvation using the air amplifier. This is explained by a mechanism in which the air amplifier rapidly creates very small droplets from the initial ESI droplets and these microdroplets then desolvate without a significant decrease in pH, resulting in retention of the folded protein conformations. Holomyoglobin is visible at pH 3.5, a much lower value than the minimum needed to see this form in conventional ESI, providing evidence for the importance of the conditions used in the desolvation process to preserve the protein conformation. A second experiment sought to strengthen the association of serene octamer with prebiotic biochemical evolution, using a thermal method to generate noncovalent clusters from solids instead of using ESI. Spontaneously self-assembling of clusters of amino acids occurs on heating the solids in air. Serine forms clusters to an unusual extent, showing a magic number octamer on sublimation. Two isomers of vapor phase serine octamers are generated at 130°C and 220°C respectively. The higher temperature cluster shows a strong homochiral preference, as confirmed by isotopic labeling experiments. This serine cluster undergoes enantioselective substitution reactions with other amino acids. These reactions transfer the chirality of serine to the amino acid which is incorporated into the octamer. A variety of pyrolysis products of serine were observed including alanine, glycine, and ethanolamine, and these could also be incorporated into the thermally-formed serine octamers. Chiral chromatography analysis confirmed that L-serine sublimation produced DL-alanine, glycine and ethanolamine; in the presence of hydrogen sulfide L-serine yielded L-cysteine. These data support the hypothesis that serine, through its homochiral serine octamer, might have played a pivotal role in biomolecule homochirogenesis.

Degree

Ph.D.

Advisors

Cooks, Purdue University.

Subject Area

Analytical chemistry

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