Early Detection and Intervention in Audiology

"Early hearing detection and intervention (EHDI) is the gold standard for any practising audiologist, and for families of infants and children with hearing impairment. Yet EHDI remains a significant challenge for Africa, and various initiatives are in place to address this gap in transferring policy into practice within the southern African context. Early Detection and Intervention in Audiology: An African Perspective aims to address the diversity of factors in southern Africa that presents unique challenges to teaching and research in this field. The South African government’s heightened focus on increasing access to health care, which includes ongoing Early Childhood Development (ECD) programmes, makes this an opportune time for establishing and documenting evidence-based research for current undergraduate and postgraduate students. Detailed case studies pay careful attention to contextual relevance and responsiveness to both identification and intervention in hearing impairment. With diverse contributions from local and international experts, but always with an African perspective, this textbook will be an essential resource for students, researchers and practitioners.

A REDOR ssNMR Investigation of the Role of an N‑Terminus Lysine in R5 Silica Recognition

Diatoms are unicellular algae that construct cell walls called frustules by the precipitation of silica, using special proteins that order the silica into a wide variety of nanostructures. The diatom species <i>Cylindrotheca fusiformis</i> contains proteins called silaffins within its frustules, which are believed to assemble into supramolecular matrices that serve as both accelerators and templates for silica deposition. Studying the properties of these biosilicification proteins has allowed the design of new protein and peptide systems that generate customizable silica nanostructures, with potential generalization to other mineral systems. It is essential to understand the mechanisms of aggregation of the protein and its coprecipitation with silica. We continue previous investigations into the peptide R5, derived from silaffin protein sil1p, shown to independently catalyze the precipitation of silica nanospheres in vitro. We used the solid-state NMR technique ¹³C­{²⁹Si} and ¹⁵N­{²⁹Si} REDOR to investigate the structure and interactions of R5 in complex with coprecipitated silica. These experiments are sensitive to the strength of magnetic dipole–dipole interactions between the ¹³C nuclei in R5 and the ²⁹Si nuclei in the silica and thus yield distance between parts of R5 and ²⁹Si in silica. Our data show strong interactions and short internuclear distances of 3.74 ± 0.20 Å between ¹³CO Lys3 and silica. On the other hand, the C_α and C_β nuclei show little or no interaction with ²⁹Si. This selective proximity between the K3 CO and the silica supports a previously proposed mechanism of rapid silicification of the antimicrobial peptide KSL (KKVVFKVKFK) through an imidate intermediate. This study reports for the first time a direct interaction between the N-terminus of R5 and silica, leading us to believe that the N-terminus of R5 is a key component in the molecular recognition process and a major factor in silica morphogenesis

Comparative Study of Secondary Structure and Interactions of the R5 Peptide in Silicon Oxide and Titanium Oxide Coprecipitates Using Solid-State NMR Spectroscopy

A biomimetic, peptide-mediated approach to inorganic nanostructure formation is of great interest as an alternative to industrial production methods. To investigate the role of peptide structure on silica (SiO₂) and titania (TiO₂) morphologies, we use the R5 peptide domain derived from the silaffin protein to produce uniform SiO₂ and TiO₂ nanostructures from the precursor silicic acid and titanium bis­(am­monium lac­tato)­di­hydroxide, respectively. The resulting biosilica and biotitania nanostructures are characterized using scanning electron microscopy. To investigate the process of R5-mediated SiO₂ and TiO₂ formation, we carry out 1D and 2D solid-state NMR (ssNMR) studies on R5 samples with uniformly ¹³C- and ¹⁵N-labeled residues to determine the backbone and side-chain chemical shifts. ¹³C chemical shift data are in turn used to determine peptide backbone torsion angles and secondary structure for the R5 peptide neat, in silica, and in titania. We are thus able to assess the impact of the different mineral environments on peptide structure, and we can further elucidate from ¹³C chemical shifts change the degree to which various side chains are in close proximity to the mineral phases. These comparisons add to the understanding of the role of R5 and its structure in both SiO₂ and TiO₂ formation

A Study of Phenylalanine Side-Chain Dynamics in Surface-Adsorbed Peptides Using Solid-State Deuterium NMR and Rotamer Library Statistics

Extracellular matrix proteins adsorbed onto mineral surfaces exist in a unique environment where the structure and dynamics of the protein can be altered profoundly. To further elucidate how the mineral surface impacts molecular properties, we perform a comparative study of the dynamics of nonpolar side chains within the mineral-recognition domain of the biomineralization protein salivary statherin adsorbed onto its native hydroxyapatite (HAP) mineral surface versus the dynamics displayed by the native protein in the hydrated solid state. Specifically, the dynamics of phenylalanine side chains (viz., F7 and F14) located in the surface-adsorbed 15-amino acid HAP-recognition fragment (SN15: DpSpSEEKFLRRIGRFG) are studied using deuterium magic angle spinning (²H MAS) line shape and spin–lattice relaxation measurements. ²H NMR MAS spectra and <i>T</i>₁ relaxation times obtained from the deuterated phenylalanine side chains in free and HAP-adsorbed SN15 are fitted to models where the side chains are assumed to exchange between rotameric states and where the exchange rates and a priori rotameric state populations are varied iteratively. In condensed proteins, phenylalanine side-chain dynamics are dominated by 180° flips of the phenyl ring, i.e., the “π flip”. However, for both F7 and F14, the number of exchanging side-chain rotameric states increases in the HAP-bound complex relative to the unbound solid sample, indicating that increased dynamic freedom accompanies introduction of the protein into the biofilm state. The observed rotameric exchange dynamics in the HAP-bound complex are on the order of 5–6 × 10⁶ s^–1, as determined from the deuterium MAS line shapes. The dynamics in the HAP-bound complex are also shown to have some solution-like behavioral characteristics, with some interesting deviations from rotameric library statistics

Diatom Mimics: Directing the Formation of Biosilica Nanoparticles by Controlled Folding of Lysine-Leucine Peptides

Silaffins, long chain polyamines, and other biomolecules found in diatoms are involved in the assembly of a large number of silica nanostructures under mild, ambient conditions. Nanofabrication researchers have sought to mimic the diatom’s biosilica production capabilities by engineering proteins to resemble aspects of naturally occurring biomolecules. Such mimics can produce monodisperse biosilica nanospheres, but in vitro production of the variety of intricate biosilica nanostructures that compose the diatom frustule is not yet possible. In this study we demonstrate how LK peptides, composed solely of lysine (K) and leucine (L) amino acids arranged with varying hydrophobic periodicities, initiate the formation of different biosilica nanostructures in vitro. When L and K residues are arranged with a periodicity of 3.5 the α-helical form of the LK peptide produces monodisperse biosilica nanospheres. However, when the LK periodicity is changed to 3.0, corresponding to a 3₁₀ helix, the morphology of the nanoparticles changes to elongated rod-like structures. β-strand LK peptides with a periodicity of 2.0 induce wire-like silica morphologies. This study illustrates how the morphology of biosilica can be changed simply by varying the periodicity of polar and nonpolar amino acids

Serine–Lysine Peptides as Mediators for the Production of Titanium Dioxide: Investigating the Effects of Primary and Secondary Structures Using Solid-State NMR Spectroscopy and DFT Calculations

A biomimetic approach to the formation of titania (TiO₂) nanostructures is desirable because of the mild conditions required in this form of production. We have identified a series of serine–lysine peptides as candidates for the biomimetic production of TiO₂ nanostructures. We have assayed these peptides for TiO₂-precipitating activity upon exposure to titanium bis­(ammonium lactato)­dihydroxide and have characterized the resulting coprecipitates using scanning electron microscopy. A subset of these assayed peptides efficiently facilitates the production of TiO₂ nanospheres. Here, we investigate the process of TiO₂ nanosphere formation mediated by the S–K peptides KSSKK- and SKSK₃SKS using one-dimensional and two-dimensional solid-state NMR (ssNMR) on peptide samples with uniformly ¹³C-enriched residues. ssNMR is used to assign ¹³C chemical shifts (CSs) site-specifically in each free peptide and TiO₂-embedded peptide, which are used to derive secondary structures in the neat and TiO₂ coprecipitated states. The backbone ¹³C CSs are used to assess secondary structural changes undergone during the coprecipitation process. Side-chain ¹³C CS changes are analyzed with density functional theory calculations and used to determine side-chain conformational changes that occur upon coprecipitation with TiO₂ and to determine surface orientation of lysine side chains in TiO₂–peptide composites

Direct Observation of Phenylalanine Orientations in Statherin Bound to Hydroxyapatite Surfaces

Extracellular biomineralization proteins such as salivary statherin control the growth of hydroxyapatite (HAP), the principal component of teeth and bones. Despite the important role that statherin plays in the regulation of hard tissue formation in humans, the surface recognition mechanisms involved are poorly understood. The protein–surface interaction likely involves very specific contacts between the surface atoms and the key protein side chains. This study demonstrates for the first time the power of combining near-edge X-ray absorption fine structure (NEXAFS) spectroscopy with element labeling to quantify the orientation of individual side chains. In this work, the 15 amino acid N-terminal binding domain of statherin has been adsorbed onto HAP surfaces, and the orientations of phenylalanine rings F7 and F14 have been determined using NEXAFS analysis and fluorine labels at individual phenylalanine sites. The NEXAFS-derived phenylalanine tilt angles have been verified with sum frequency generation spectroscopy