Ted Mau

Structure of alpha-lytic protease complexed with its pro region.

While the majority of proteins fold rapidly and spontaneously to their native states, the extracellular bacterial protease α-lytic protease (αLP) has a t1/2 for folding of ~2,000 years, corresponding to a folding barrier of 30 kcal mol–1. αLP is synthesized as a pro-enzyme where its pro region (Pro) acts as a foldase to stabilize the transition state for the folding reaction. Pro also functions as a potent folding catalyst when supplied as a separate polypeptide chain, accelerating the rate of αLP folding by a factor of 3 × 109. In the absence of Pro, αLP folds only partially to a stable molten globule-like intermediate state. Addition of Pro to this intermediate leads to rapid formation of native αLP. Here we report the crystal structures of Pro and of the non-covalent inhibitory complex between Pro and native αLP. The C-shaped Pro surrounds the C-terminal ß-barrel domain of the folded protease, forming a large complementary interface. Regions of extensive hydration in the interface explain how Pro binds tightly to the native state, yet even more tightly to the folding transition state. Based on structural and functional data we propose that a specific structural element in αLP is largely responsible for the folding barrier and suggest how Pro can overcome this barrier.

Salt bridge relay triggers defective LDL receptor binding by a mutant apolipoprotein.

BACKGROUND Apolipoprotein-E (apo-E), a 34kDa blood plasma protein, plays a key role in directing cholesterol transport via its interaction with the low density lipoprotein (LDL) receptor. The amino-terminal domain of apo-E forms an unusually elongated four-helix bundle arranged such that key basic residues involved in LDL receptor binding form a cluster at the end of one of the helices. A common apo-E variant, apo-E2, corresponding to the single-site substitution Arg158-->Cys, displays minimal LDL receptor binding and is associated with significant changes in plasma cholesterol levels and increased risk of coronary heart disease. Surprisingly, the site of mutation in this variant is physically well removed (> 12A) from the cluster of LDL receptor binding residues. RESULTS We now report the refined crystal structure of the amino-terminal domain of apo-E2, at a nominal resolution of 3.0A. This structure reveals significant conformational changes relative to the wild-type protein that may account for reduced LDL receptor binding. Removal of the Arg158 side chain directly disrupts a pair of salt bridges, causing a compensatory reorganization of salt bridge partners that dramatically alters the charge surface presented by apo-E to its receptor. CONCLUSIONS It is proposed that the observed reorganization of surface salt bridges is responsible for the decreased receptor binding by apo-E2. This reorganization, essentially functioning as a mutationally induced electrostatic switch to turn off receptor binding, represents a novel mechanism for the propagation of conformational changes over significant distances.

Factors associated with voice therapy outcomes in the treatment of presbyphonia.

Age, vocal fold atrophy, glottic closure pattern, and the burden of medical problems are associated with voice therapy outcomes for presbyphonia.

Diagnostic Evaluation and Management of Hoarseness

Hoarseness is a common symptom that can result from a wide spectrum of underlying causes ranging from the common cold to a malignancy. A framework for diagnostic evaluation is presented based on categorizing the myriad of causes by how they interfere with the voice production mechanism. Triaging of cases by necessity or urgency of laryngoscopy is assisted by forming a global index of suspicion based on targeted history taking. Laryngoscopy is required in most cases to obtain a diagnosis for the hoarseness. Treatments commonly prescribed for hoarseness are critically examined in this article. To listen to audio clips of patients with different types of hoarseness, please visit our website, www.medical.theclinics.com.

Cadaveric and engineering analysis of the septal L-strut

Objectives: To identify patterns of failure of the L‐strut, to identify elements of the nasal framework that support the L‐strut, and to investigate the effect of altering L‐strut design on its stability.

Viscoelastic properties of phonosurgical biomaterials at phonatory frequencies

The purpose of this study was to examine the functional biomechanical properties of several injectable biomaterials currently or potentially used for vocal fold augmentation.

Predicting Achievable Fundamental Frequency Ranges in Vocalization Across Species

Vocal folds are used as sound sources in various species, but it is unknown how vocal fold morphologies are optimized for different acoustic objectives. Here we identify two main variables affecting range of vocal fold vibration frequency, namely vocal fold elongation and tissue fiber stress. A simple vibrating string model is used to predict fundamental frequency ranges across species of different vocal fold sizes. While average fundamental frequency is predominantly determined by vocal fold length (larynx size), range of fundamental frequency is facilitated by (1) laryngeal muscles that control elongation and by (2) nonlinearity in tissue fiber tension. One adaptation that would increase fundamental frequency range is greater freedom in joint rotation or gliding of two cartilages (thyroid and cricoid), so that vocal fold length change is maximized. Alternatively, tissue layers can develop to bear a disproportionate fiber tension (i.e., a ligament with high density collagen fibers), increasing the fundamental frequency range and thereby vocal versatility. The range of fundamental frequency across species is thus not simply one-dimensional, but can be conceptualized as the dependent variable in a multi-dimensional morphospace. In humans, this could allow for variations that could be clinically important for voice therapy and vocal fold repair. Alternative solutions could also have importance in vocal training for singing and other highly-skilled vocalizations.

Phonation Threshold Pressure and Flow in Excised Human Larynges

To determine the phonation threshold pressure (PTP) and phonation threshold flow (PTF) in excised human larynges; determine the effects of posterior glottal width, glottal area, and gender on PTP and PTF; test the hypothesis that hysteresis is present in excised human laryngeal phonation; and compare these results to those from canine experiments and human subject measurements.

A randomized controlled trial of stretch-and-flow voice therapy for muscle tension Dysphonia

To investigate the effect of stretch‐and‐flow voice therapy on vocal function and handicap.

Influence of gender and injection site on vocal fold augmentation

OBJECTIVE: To determine the influence of gender and injection site on the amount of injectate needed to medialize an immobile vocal fold, and to describe the distribution patterns of the injected bolus. STUDY DESIGN: Surgical intervention in human cadaveric larynges in experimental setting. SUBJECTS AND METHODS: Cadaveric larynges were injected with calcium hydroxylapatite into the lateral or medial aspect of the vocal fold. High-resolution CT scans were obtained before and after injection. RESULTS: Males required 50% to 60% more material than females (P = 0.03). For both genders, lateral injections required more than medial injections (P < 0.001). Laterally injected boluses tended to distribute toward the cricothyroid space, with frank extrusions more common in females. CONCLUSION: The amount of injectate required to medialize male and female vocal folds is significantly different. The smaller size of the female larynx likely accounts for a higher incidence of extrusion through the cricothyroid space. These gender differences should be taken into consideration when performing injection laryngoplasty.