Hydrogen bond rotations as a uniform structural tool for analyzing protein architecture

Proteins fold into three-dimensional structures, which determine their diverse functions. The conformation of the backbone of each structure is locally at each Cα effectively described by conformational angles resulting in Ramachandran plots. These, however, do not describe the conformations around hydrogen bonds, which can be non-local along the backbone and are of major importance for protein structure. Here, we introduce the spatial rotation between hydrogen bonded peptide planes as a new descriptor for protein structure locally around a hydrogen bond. Strikingly, this rotational descriptor sampled over high-quality structures from the protein data base (PDB) concentrates into 30 localized clusters, some of which correlate to the common secondary structures and others to more special motifs, yet generally providing a unifying systematic classification of local structure around protein hydrogen bonds. It further provides a uniform vocabulary for comparison of protein structure near hydrogen bonds even between bonds in different proteins without alignment

Indications of Radiation Damage in Ferredoxin Microcrystals using High-Intensity X-FEL Beams

Proteins that contain metal cofactors are expected to be highly radiation sensitive since the degree of X-ray absorption correlates with the presence of high-atomic-number elements and X-ray energy. To explore the effects of local damage in serial femtosecond crystallography (SFX), Clostridium ferredoxin was used as a model system. The protein contains two [4Fe-4S] clusters that serve as sensitive probes for radiation-induced electronic and structural changes. High-dose room-temperature SFX datasets were collected at the Linac Coherent Light Source of ferredoxin microcrystals. Difference electron density maps calculated from high-dose SFX and synchrotron data show peaks at the iron positions of the clusters, indicative of decrease of atomic scattering factors due to ionization. The electron density of the two [4Fe-4S] clusters differs in the FEL data, but not in the synchrotron data. Since the clusters differ in their detailed architecture, this observation is suggestive of an influence of the molecular bonding and geometry on the atomic displacement dynamics following initial photoionization. The experiments are complemented by plasma code calculations

Stock Market Reaction to Unexpected Growth in Marketing Expenditure: Negative for Sales Force, Contingent on Spending Level for Advertising

Because firms do not publicly report marketing expenditures, most studies of the link between firm value and marketing consider advertising (which is publicly reported for many firms) a proxy for marketing. The authors extend those studies in two ways. First, they broaden the proxy for marketing by considering both advertising and sales force. Second, they offer an explanation for the fact that some studies linking advertising to firm value find a positive relationship, whereas others find a negative relationship. The accounting literature suggests that the link to firm value for both unexpected growth in sales force expenditures and unexpected growth in advertising expenditures should be negative. The authors confirm the hypothesized accounting relationship for sales force expenditures but find a contingent relationship for advertising expenditures. Firm value and unexpected growth in advertising expenditures are negatively related for firms that advertise below the advertising response threshold, but they are positively related for firms that advertise above that threshold. Perhaps because this contingent relationship is difficult for analysts to learn through observation of the stock market, analysts ignore value-relevant advertising expenditure information when they forecast firm valueclos