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Mass spectrometry in combination with protein charge ladders is used to examine the relationship between the surface charge and hydrophobicity of a representative globular protein (bovine carbonic anhydrase II; BCA II) and its rate of amide hydrogen-deuterium (H/D) exchange. The similarities between the rates of H/D exchange for the perbutyrated BCA II and peracetylated BCA II indicated that the electrostatic charge play a more significant role than the hydrophobicity of surface groups in determining the rate of H/D exchange.

This paper combines two techniques—mass spectrometry and protein charge ladders—to examine the relationship between the surface charge and hydrophobicity of a protein (bovine carbonic anhydrase II; BCA II) and its rate of amide hydrogen-deuterium (H/D) exchange. Mass spectrometric analysis indicated that the sequential acetylation of surface lysine-\(\epsilon\)-NH\(_{3}\)\(^{+}\) groups—a type of modification that increases the net negative charge and hydrophobicity of the surface of BCA II without affecting its 2° or 3° structure—resulted in a linear increase in the total number of backbone amide hydrogen that are protected from exchange with solvent (2 h, pD 7.4, 15 ºC). Each successive acetylation produced BCA II proteins with one additional hydrogen protected after two hours in deuterated buffer (pD 7.4, 15 ºC). NMR spectroscopy demonstrated that these protected hydrogen atoms were not located on the side chain of the acetylated lysine residues (i.e., lys-\(\epsilon\)-NHCOCH\(_{3}\)). The decrease in rate of exchange associated with acetylation paralleled a decrease in thermostability: the most slowly exchanging rungs were the least thermostable (as measured by differential scanning calorimetry). The fact that the rates of H/D exchange were similar for perbutyrated BCA II (e.g., [lys-\(\epsilon\)-NHCO(CH\(_{2}\))\(_{2}\)CH\(_{3}\)]\(_{18}\)) and peracetylated BCA II (e.g., [lys-\(\epsilon\)-NHCOCH\(_{3}\)]\(_{18}\)) suggests that the charge is more important than the hydrophobicity of surface groups in determining the rate of H/D exchange. These kinetic electrostatic effects could complicate the interpretation of experiments in which H/D exchange methods are used to probe the structural effects of non-isoelectric perturbations to proteins (i.e., phosphorylation, acetylation, or the binding of the protein to an oligonucleotide or another charged ligand or protein)., Chemistry and Chemical Biology

This paper describes a photolithographic method to create sub-micron-scale patterns of cation-cross-linked poly(acrylic acid) (CCL-PAA). PAA can be cross-linked with a wide range of metal cations-including, but not limited to, Ag, Ca, Pd, Al, La, and Ti. Upon patterning a positive photoresist (diazonaphthoquinone-novolac resin) on a film of CCL-PAA, the exposed regions of CCL-PAA were etched by either an aqueous NaOH or EDTA solution. The initial cross-linking cation could be exchanged for a second cation that could not be patterned photolithographically. We used these patterned films of CCL-PAA i) to host and template the reduction of metallic cations to metallic nanoparticles, and ii) to fabricate porous, low- dielectric substrates.