Dynamics of Dystrophin's Actin-Binding Domain.

We have used pulsed electron paramagnetic resonance, calorimetry, and molecular dynamics simulations to examine the structural mechanism of binding for dystrophin's N-terminal actin-binding domain (ABD1) and compare it to utrophin's ABD1. Like other members of the spectrin superfamily, dystrophin's ABD1 consists of two calponin-homology (CH) domains, CH1 and CH2. Several mutations within dystrophin's ABD1 are associated with the development of severe degenerative muscle disorders Duchenne and Becker muscular dystrophies, highlighting the importance of understanding its structural biology.

Structural Impact of Phosphorylation and Dielectric Constant Variation on Synaptotagmin's IDR.

We used time-resolved Förster resonance energy transfer, circular dichroism, and molecular dynamics simulation to investigate the structural dependence of synaptotagmin 1's intrinsically disordered region (IDR) on phosphorylation and dielectric constant. We found that a peptide corresponding to the full-length IDR sequence, a ∼60-residue strong polyampholyte, can sample structurally collapsed states in aqueous solution, consistent with its κ-predicted behavior, where κ is a sequence-dependent parameter that is used to predict IDR compaction. In implicit solvent simulations of this same sequence, lowering the dielectric constant to more closely mimic the environment near a lipid bilayer surface promoted further sampling of collapsed structures.

Structural basis for high-affinity actin binding revealed by a β-III-spectrin SCA5 missense mutation.

Spinocerebellar ataxia type 5 (SCA5) is a neurodegenerative disease caused by mutations in the cytoskeletal protein β-III-spectrin. Previously, a SCA5 mutation resulting in a leucine-to-proline substitution (L253P) in the actin-binding domain (ABD) was shown to cause a 1000-fold increase in actin-binding affinity. However, the structural basis for this increase is unknown.

Synaptotagmin I's Intrinsically Disordered Region Interacts with Synaptic Vesicle Lipids and Exerts Allosteric Control over C2A.

Synaptotagmin I (Syt I) is a vesicle-localized integral membrane protein that senses the calcium ion (Ca(2+)) influx to trigger fast synchronous release of neurotransmitter. How the cytosolic domains of Syt I allosterically communicate to propagate the Ca(2+) binding signal throughout the protein is not well understood. In particular, it is unclear whether the intrinsically disordered region (IDR) between Syt I's transmembrane helix and first C2 domain (C2A) plays an important role in allosteric modulation of Ca(2+) binding.

Randomly organized lipids and marginally stable proteins: a coupling of weak interactions to optimize membrane signaling.

Eukaryotic lipids in a bilayer are dominated by weak cooperative interactions. These interactions impart highly dynamic and pliable properties to the membrane. C2 domain-containing proteins in the membrane also interact weakly and cooperatively giving rise to a high degree of conformational plasticity.

Allostery and instability in the functional plasticity of synaptotagmin I.

Synaptotagmin I (Syt I) is the calcium ion sensor for regulated release of neurotransmitter. How Syt I mediates this cellular event has been a question of extensive study for decades and yet, a clear understanding of the protein's diverse functionality has remained elusive. Using tools of thermodynamics, we have identified two intrinsic properties that may account for Syt I's functional plasticity: marginal stability and negative coupling.

Negative coupling as a mechanism for signal propagation between C2 domains of synaptotagmin I.

Synaptotagmin I (Syt I) is a vesicle-localized protein implicated in sensing the calcium influx that triggers fast synchronous release of neurotransmitter. How Syt I utilizes its two C2 domains to integrate signals and mediate neurotransmission has continued to be a controversial area of research, though prevalent hypotheses favor independent function. Using differential scanning calorimetry and fluorescence lifetime spectroscopy in a thermodynamic denaturation approach, we tested an alternative hypothesis in which both domains interact to cooperatively disseminate binding information.

Unicommissural aortic valves: gross, histological, and immunohistochemical analysis of 52 cases (1978-2008).

Background: Unicommissural aortic valves (UAVs) are rare anomalies in which adjacent cusps of two commissures are congenitally fused. Currently, features of UAVs are poorly characterized.

Methods: Fifty-two surgical and autopsy cases of UAV at Mayo Clinic were evaluated for various clinicopathologic features.

Original research in the classroom: why do zebrafish spawn in the morning?

As part of an upper level undergraduate developmental biology course at the University of Minnesota Duluth, we developed a unit in which students carried out original research as part of a cooperative class project. Students had the opportunity to gain experience in the scientific method from experimental design all of the way through to the preparation of publication on their research that included text, figures, and tables. This kind of inquiry-based learning has been shown to have many benefits for students, including increased long-term learning and a better understanding of the process of scientific discovery.

MGMT promoter methylation and immunoexpression in aggressive pituitary adenomas and carcinomas.

MGMT promoter hypermethylation of aggressive pituitary adenomas and pituitary carcinomas and low protein expression are implicated in improved response to treatment with temozolomide (TMZ). The aim of the present study was to investigate MGMT promoter methylation and immunoexpression in an aggressive subset of pituitary adenomas and carcinomas. Our material consisted of 12 silent subtype 3 (SS3) adenomas, 10 primary carcinomas, and 4 disseminated metastases.

MGMT immunoexpression in silent subtype 3 pituitary adenomas: possible therapeutic implications.

The objective of the study was to assess O(6)-methylguanine-DNA methyltransferase (MGMT) immunoreactivity in pituitary adenomas of silent subtype 3 as a potential indicator of temozolomide susceptibility. The Mayo Clinic Anatomic Pathology Database was searched for all cases of silent subtype 3 pituitary adenoma. Each of the 23 cases identified had been confirmed on the basis of histology, immunohistochemical staining for pituitary hormones, as well as on diagnostic ultrastructural criteria.

Prosthetic valve endocarditis: clinicopathological correlates in 122 surgical specimens from 116 patients (1985-2004).

Background: Few studies have documented the clinicopathological features of prosthetic valve endocarditis independently of native valve endocarditis.

Study Design: Retrospective analysis of patients undergoing cardiac surgery for prosthetic valve endocarditis at our institution (1985-2004).

Methods: Medical records and microscopic slides were reviewed from 116 patients for demographics, infecting organisms, comorbidities, and pathologic features.

Echocardiographic features of cardiac amyloidosis presenting as endomyocardial disease in a 54-year-old male.

Although primary cardiac amyloidosis is a rare affliction of the heart, its clinical and pathology features have been well described. Patients generally present with exertional dyspnea, chest discomfort, or congestive heart failure. Cardiac imaging typically reveals ventricular wall thickening, systolic and diastolic dysfunction, valvular thickening, and pericardial effusion.

Congenital aortic sinus aneurysm causing sudden unexpected death in a 56-year-old woman.

Sudden unexpected death due to hemopericardium generally has 2 main causes, rupture of the ascending aorta or rupture of a transmural myocardial infarct. We report an unusual cause of fatal hemopericardium in a 56-year-old woman that occurred in the setting of a motor vehicle mishap.At autopsy, 300 mL of blood were present in the pericardial sac, due to rupture of a previously undetected congenital aortic sinus aneurysm.

Complications of endovascular polymers associated with vascular introducer sheaths and metallic coils in 3 patients, with literature review.

Background: Hydrophilic coatings on arterial introducer sheaths reduce the frequency of spasm during cardiac catheterization. Moreover, during treatment of cerebral artery aneurysms, hydrophilic coatings on microcatheters ease their maneuverability, and polymers within embolization coils enhance neointimal fibrosis at the aneurysm neck. Foreign-body giant cell reactions can result when a polymer is stripped from its source.

Hamartomas of mature cardiac myocytes: report of 7 new cases and review of literature.

Only 8 cases of hamartomas of mature cardiac myocytes have been reported. The aim of the study was to describe 7 new cases and provide clinicopathologic correlation. Our anatomical pathology database was searched for all cases of cardiac hamartoma, of which 7 represented mature myocyte type.

Neuronal ceroid lipofuscinosis in a 31-year-old woman presenting as biventricular heart failure with restrictive features.

A 31-year-old woman presented with dyspnea and left-sided chest discomfort and was found to have biventricular heart failure with impaired ventricular filling. Clinically, she was thought to have restrictive cardiomyopathy or constrictive pericarditis. Transmission electron microscopy of myocardial tissue unexpectedly revealed crosshatched, curvilinear, and fingerprint depositions, which were characteristic for neuronal ceroid lipofuscinosis.

Beta-catenin mutations do not contribute to cardiac fibroma pathogenesis.

Cardiac fibromas are the 2nd most common benign cardiac tumor occurring in children and bear a striking morphologic resemblance to soft tissue or desmoid fibromatosis. Since activating mutations in beta-catenin are common in desmoid fibromatosis as well as other spindle cell proliferations, the aim of our study was to determine if such mutations could be identified in cardiac fibroma. Nine cardiac fibromas from patients with surgical resection were examined for beta-catenin mutations by immunoperoxidase staining for beta-catenin protein and DNA sequencing of a region in exon 3 of the beta-catenin gene, where relatively conserved mutations have been described in desmoid fibromatosis.

Recurrent cardiac calcific amorphous tumor: the CAT had a kitten.

Background: Cardiac calcified amorphous tumors (CATs) represent degenerating intracavitary mural thrombi that can mimic neoplasms and cause symptoms due to embolization or obstruction. Surgical excision is generally curative. Postoperative recurrences have not been previously reported.

Primary cardiac amyloidosis with 20-year survival.

Background: The natural history of primary amyloidosis is poor, and for patients with symptomatic cardiac involvement, survival is generally less than 6 months. Even among treated patients with amyloid heart disease, survival beyond 5 years is rare.

Case Report: We report a patient with primary cardiac amyloidosis who is currently alive 20 years after his initial diagnosis.