Surface residues dynamically organize water bridges to enhance electron transfer between proteins

Cellular energy production depends on electron transfer (ET) between proteins. In this theoretical study, we investigate the impact of structural and conformational variations on the electronic coupling between the redox proteins methylamine dehydrogenase and amicyanin from Paracoccus denitrificans. We used molecular dynamics simulations to generate configurations over a duration of 40 ns (sampled at 100-fs intervals) in conjunction with an ET pathway analysis to estimate the ET coupling strength of each configuration. In the wild-type complex, we find that the most frequently occurring molecular configurations afford superior electronic coupling due to the consistent presence of a water molecule hydrogen-bonded between the donor and acceptor sites. We attribute the persistence of this water bridge to a “molecular breakwater” composed of several hydrophobic residues surrounding the acceptor site. The breakwater supports the function of nearby solvent-organizing residues by limiting the exchange of water molecules between the sterically constrained ET region and the more turbulent surrounding bulk. When the breakwater is affected by a mutation, bulk solvent molecules disrupt the water bridge, resulting in reduced electronic coupling that is consistent with recent experimental findings. Our analysis suggests that, in addition to enabling the association and docking of the proteins, surface residues stabilize and control interprotein solvent dynamics in a concerted way.     

Testing a typology of batterers

A. Holtzworth-Munroe and G. L. Stuart (1994) proposed a tripartite typology of men who batter their female partners based on the severity of violence, extent of violence, and personality disorder characteristics. The current study attempts to empirically validate this typology using data from 75 domestically violent (DV) men and their partners, and 32 maritally distressed, nonviolent (DNV) comparison couples. Mixture analysis results generally supported the model, although 2 types were not distinguishable on personality disorder characteristics as predicted. Generally violent batterers were significantly more violent within and outside the relationship. The pathological group was moderately violent within and outside the relationship and endorsed numerous psychological symptoms. Family-only batterers endorsed fewer symptoms and were less violent. Violence in the family of origin, attachment, and communication skills also differentiated the 3 types and DNV men.     

Infarction of an accessory spleen causing an acute abdomen

A case is presented of a five year old girl in whom an acute surgical abdomen developed due to torsion and infarction of an accessory spleen. Other similar cases in the literature are reviewed. The incidence, location, and embryologic aspects of accessory spleens are discussed. Infarction of an accessory spleen, although rarely the cause of an acute surgical abdomen, should be considered in the differential diagnosis.     

Hepatic transaminase in protein-restricted rats: development of a controlled model

A marginal protein malnutrition model which makes allowances for the increasing nutritional requirements of the growing rat and the effects of dietary manipulation on diurnal rhythms, while still rigidly controlling the level of protein restriction, is reported. A predetermined, constantly increasing intake of four purified diets, providing approximately 40 to 160% of the National Research Council protein requirement for rats was fed to rats receiving a nitrogen-free energy source adlibitum. This standardization reduced within-group variation and allowed precise growth reproducibility. Biochemical parameters were measured at evenly spaced intervals throughout the day to remove diurnal differences from between-group comparisons. Growth, nitrogen balance, and 24-hour means of liver weight, DNA, RNA, protein, and glutamate-oxaloacetate and glutamate-pyruvate transaminases reflected protein intake. However, when growth was depressed 10, 30, or 60%, liver GPT/DNA was depressed 40, 49, or 67%, respectively. Hepatic GPT appears to be a sensitive and accurate indicator of marginal protein malnutrition.     

Use of sagittal images for localization of the subthalamic nucleus. Technical note

Direct observation of the subthalamic nucleus (STN) is not always possible, and physicians at many centers rely on indirect methods that relate the position of the STN to more easily recognized structures such as the red nucleus (RN). In this paper the authors describe an indirect method of viewing the STN based on the anatomy depicted on sagittal magnetic resonance (MR) images. A review of sagittal slices appearing in standard stereotactic atlases showed that the STN lies within the angle formed by the descending internal capsule (IC) and the substantia nigra (SN). The authors' technique consists of marking the location of the STN in this nigrocapsular angle on each sagittal MR image between the RN and the lateral border of the brainstem, and transferring these points to axial MR images to build a locus of points used to describe the STN. A point is chosen in the center of this locus as the stereotactic target. Two hundred eighty-two sagittal images obtained from 71 MR imaging studies performed in 29 patients by using a fast-spin echo inversion-recovery technique were examined for the presence of the STN, the SN, and the IC. The descending IC could be detected in 97% of the slices, the SN in 95% of the slices, and the STN in 73% of the slices. This indirect method involving sagittal anatomy can be used to refine localization of the STN.