Canine parvovirus capsid structure, analyzed at 2.9 A resolution

The DNA-containing capsid of canine parvovirus (CPV) is analyzed following atomic refinement at 2.9 A resolution. The capsid contains 60 copies of the capsid protein related by icosahedral symmetry. The atomic model has been extended from the first residue (Gly37) of the unrefined 3.25 A structure towards the N terminus. The electron density shows that approximately 87% of the capsid proteins have N termini on the inside of the capsid, but for approximately 13%, the polypeptide starts on the outside and runs through one of the pores surrounding each 5-fold axis, explaining apparently conflicting antigenic data. Analysis of potential hydrogen bonds reveals approximately 50% more secondary structure than previously apparent. Most of the additional secondary structure are in the 71 and 221 residue-long loop insertions between beta-strands E and F and G and H, forming subunit-bridging sheets that likely add specificity to assembly interactions. Structural analysis of the extensive subunit interactions around the 3-fold axes shows that assembly is a multistep process with loops intertwining following initial contact. Estimated free energies of association suggest that the formation of 3 and 5-fold contacts likely takes precedence over 2-fold interactions. Energies for initial association into trimers or pentamers would be similar, but the intertwining of loops about the 3-fold axis adds an additional large activation barrier to dissociation. Analysis of the surfaces of the assembled capsid shows a surprising lack of basic amino acids that might have been expected to interact with the negatively charged phosphoribose backbone of the DNA. Instead, uncharged polar and van der Waal's interactions predominate in the packaging of single-stranded DNA into the capsid.     

Magnetic resonance imaging in lactic acidosis

Mitochondrial defects, defects in gluconeogenesis, and biotin-responsive multiple carboxylase deficiency are disorders characterized by primary lactic acidosis. In this review, characteristic findings in magnetic resonance imaging (MRI) of the brain, as related to histopathological abnormalities, are described for the different disorders and the diagnostic value of the MRI findings is discussed. Inborn errors of metabolism with primary lactic acidosis should be considered in particular when MRI shows lesions similar to or reminiscent of effects of focal or generalized hypoxia-ischaemia, or when MRI shows signs of chronic neurodegeneration, but rarely in cases with predominantly white-matter changes.     

Fast and one-step folding of closely and distantly related homologous proteins of a four-helix bundle family

Bovine acyl-coenzyme A binding protein is a four-helix bundle protein belonging to a group of homologous eukaryote proteins that binds medium and long-chain acyl-coenzyme A esters with a very high affinity. The three-dimensional structure of both the free and the ligated protein together with the folding kinetics have been described in detail for the bovine protein and with four new sequences reported here, a total of 16 closely related sequences ranging from yeasts and plants to human are known. The kinetics of folding and unfolding in different concentrations of guanidine hydrochloride together with equilibrium unfolding have been measured for bovine, rat and yeast acyl-coenzyme A binding protein. The bovine and rat sequences are closely related whereas the yeast is more distantly related to these. In addition to the three natural variants, kinetics of a bovine mutant protein, Tyr31 --> Asn, have been studied. Both the folding and unfolding rates in water of the yeast protein are 15 times faster than those of bovine. The folding rates in water of the two mammalian forms, rat and bovine, are similar, though still significantly different. A faster unfolding rate both for rat and the bovine mutant protein results from a lower stability of the native states of these. These hydrophobic regions, mini cores, have been identified in the three-dimensional structure of the bovine protein and found to be formed primarily by residues that have been conserved throughout the entire eukaryote evolution from yeasts to both plants and mammals as seen in the sample of 16 sequences. The conserved residues are found to stabilize helix-helix interactions and serve specific functional purposes for ligand binding. The fast one-step folding mechanism of ACBP has been shown to be a feature that seems to be maintained throughout evolution despite numerous differences in sequence and even dramatic differences in folding kinetics and protein stability. The protein study raises the question to what extent does the conserved hydrophobic residues provide a scaffold for an efficient one-step folding mechanism.     

The association rate constant for heme binding to globin is independent of protein structure

Rate constants for CO-heme binding to 35 different recombinant apomyoglobins and several other apoproteins were measured in an effort to understand the factors governing heme affinity and the velocity of the association reaction. Surprisingly, the rate constant for the binding of monomeric heme is approximately 1 x 10(8) M-1 s-1 regardless of the structure or overall affinity of the apoprotein for iron-porphyrin. Major differences between the proteins are reflected primarily in the rates of dissociation of the prosthetic group. Slow phases observed in the reaction of CO heme with excess apomyoglobin result from formation of nonspecific heme-protein complexes which must dissociate before heme can bind specifically in the heme pocket. Once the specific heme-globin complex is formed, the heme pocket rapidly collapses around the porphyrin, simultaneously forming the bond between the proximal His93 and the heme iron atom. The overall affinity of sperm whale apomyoglobin for hemin is approximately 1 x 10(14) M-1. Nonspecific hydrophobic interactions between the porphyrin and the apolar heme cavity account for a factor of 10(5)-10(7). Covalent bond formation between Fe3+ and His93(F8) provides an additional factor of 10(3)-10(4). Specific interactions with conserved amino acids in the heme pocket contribute the final factor of 10(3)-10(4).     

Benzene-induced genotoxicity in mice in vivo detected by the alkaline comet assay: reduction by CYP2E1 inhibition

Acute, severe injury of the rabbit spinal cord, induced by the weight-drop method, causes alterations of the enzyme activities related to cholinergic and energy metabolism. Morphological examinations at the trauma site show degenerative processes in neurons 0.5 hr posttrauma and a marked decrease in the number of living cells 24 hrs later. Both biochemical and cytochemical findings show that the tissue metabolic and morphologic derangement, caused by severe spinal cord injury, is mostly confined to the gray matter at an early stage (0.5 hr), whereas 24 hrs later the white matter is also involved. The decrease in choline acetyl-transferase and acetylcholinesterase activities in the gray matter parallels the impairment of complex IV (cytochrome c oxidase) of the respiratory chain and the presence of morphological alteration in neurons. The dramatic drop in the enzyme activities, observed 24 hrs after the induction of the severe trauma is clearly associated with the loss of cells.     

The effects of a left bundle-branch block on ventricular repolarization dispersion

Patients with left bundle-branch block (LBBB) often present electrocardiographic abnormalities and, therefore, are excluded from studies concerning electrocardiographic evaluation of ventricular repolarization. The aim of the study was to assess whether LBBB could influence dispersion of ventricular repolarization. Surface electrocardiograms of 16 patients (9 males and 7 females, mean age 58 +/- 14 years) with episodes of intermittent LBBB were analyzed. Six patients were affected by coronary artery disease, 6 by hypertensive cardiomyopathy and 4 by dilated cardiomyopathy. Maximal QT and JT corrected intervals, QT and JT dispersion, and QT and JT dispersion corrected for heart rate, were obtained before and after LBBB. We observed a significant prolongation of maximal QT (412 +/- 29 vs 433 +/- 25 ms; p < 0.05), and of maximal corrected QT (457 +/- 37 vs 497 +/- 56 ms; p < 0.05) after LBBB. Maximal JT interval, also corrected for heart rate, did not show any significant modification after LBBB. Moreover, we did not observe any significant difference in electrocardiographic parameters of dispersion of repolarization. Our results seem to indicate that LBBB did not alter significantly dispersion of ventricular repolarization. QT dispersion is considered an important marker of risk for incidence of ventricular arrhythmias. If our results will be confirmed in larger groups of patients, analysis of QT dispersion could be extended even to patients with LBBB.     

Dimension and related anatomical distance of Koch's triangle in patients with atrioventricular nodal reentrant tachycardia

INTRODUCTION: The dimension of Koch's triangle in patients with AV nodal reentrant tachycardia has not been well described. Understanding the dimension and anatomical distance related to Koch's triangle might be useful in avoiding accidental AV block during ablation of the slow pathway. The purposes of this study were to define the dimension of Koch's triangle and its related anatomical distance and correlate these parameters with the successful ablation sites in patients with AV nodal reentrant tachycardia. METHODS AND RESULTS: We studied 218 patients with AV nodal reentrant tachycardia. The distance between the presumed proximal His-bundle area and the base of the coronary sinus orifice (DHis-OS) measured in the right anterior oblique view was used to define the dimension of Koch's triangle. The distance of the proximal His-bundle recording site from the successful ablation site (DHis-Ab) and the distance as a fraction of the entire length of Koch's triangle (DHis-Ab/DHis-Os) were determined. The mean DHis-Os and DHis-Ab were 25.9 +/- 7.9 and 13.4 +/- 3.8 mm, respectively. DHis-Os negatively correlated with patient age (r = -0.41, P < 0.0001) and body mass index (r = -0.18, P = 0.004). Among the patients with successful ablation sites in the medial area, DHis-Os was longer (27.2 +/- 6.6 vs 24.6 +/- 8.4 mm, P < 0.005), DHis-Ab was similar (12.9 +/- 3.1 vs 13.9 +/- 4.0, P > 0.05) and DHis-Ab/DHis-Os was smaller (0.48 +/- 0.04 vs 0.74 +/- 0.11, P < 0.05). Furthermore, the patients with successful ablation sites in the medial location needed more radiofrequency pulse numbers than those in the posterior location (6 +/- 4 vs 4 +/- 3, P < 0.05). CONCLUSION: The site of successful slow pathway ablation was consistently about 13 mm from the site recording the proximal His-bundle deflection in patients with AV nodal reentrant tachycardia despite marked variability in the dimensions of Koch's triangle; therefore, patients with large triangles required ablation in the medial region rather than the posterior region. Care should be taken when delivering radiofrequency energy to the posteroseptal area in patients with shorter DHis-Os to avoid injury to AV node.     

Neuropsychiatric aspects of progressive supranuclear palsy

Administering the Neuropsychiatric Inventory (NPI), we examined the behavioral symptoms of 22 patients with progressive supranuclear palsy (PSP), 50 patients with Alzheimer's disease, and 40 controls. PSP patients exhibited apathy (91%), disinhibition (36%), dysphoria (18%) and anxiety (18%), but rarely (< 9%) irritability, abnormal motor behaviors, or agitation. Apathy in PSP was significantly associated with executive dysfunction. The presence of high apathy and low agitation and anxiety scale scores correctly identified the PSP patients 85% of the time. Evaluating the behavioral abnormalities of patients with neurodegenerative disorders will aid diagnosis and facilitate management.