To characterize keratin intermediate filament assembly mechanisms at atomic resolution, we determined the crystal structure of wild‐type human keratin‐1/keratin‐10 helix 1B heterotetramer at 3.0 Å resolution. It revealed biochemical determinants for the A11 mode of axial alignment in keratin filaments. Four regions on a hydrophobic face of the K1/K10‐1B heterodimer dictated tetramer assembly: the N‐terminal hydrophobic pocket (defined by L227K1, Y230K1, F231K1, and F234K1), the K10 hydrophobic stripe, K1 interaction residues, and the C‐terminal anchoring knob (formed by F314K1 and L318K1). Mutation of both knob residues to alanine disrupted keratin 1B tetramer and full‐length filament assembly. Individual knob residue mutant F314AK1, but not L318AK1, abolished 1B tetramer formation. The K1‐1B knob/pocket mechanism is conserved across keratins and many non‐keratin intermediate filaments. To demonstrate how pathogenic mutations cause skin disease by altering filament assembly, we additionally determined the 2.39 Å structure of K1/10‐1B containing a S233LK1 mutation linked to epidermolytic palmoplantar keratoderma. Light scattering and circular dichroism measurements demonstrated enhanced aggregation of K1S233L/K10‐1B in solution without affecting secondary structure. The K1S233L/K10‐1B octamer structure revealed S233LK1 causes aberrant hydrophobic interactions between 1B tetramers.
Transepidermal water loss (TEWL) and surface capacitance measure skin barrier permeability and skin hydration, respectively, and are frequently utilized in atopic dermatitis clinical trials. Conventional devices used to measure TEWL and hydration are often costly, bulky, and technically challenging, limiting their use to tertiary care facilities and research centers. GPSkin, a novel commercially-available device measures TEWL and skin hydration utilizing a compact, low-cost probe designed for patient operation and functions via smartphone application. This study investigated the correlation of this novel device with the Biox AquaFlux and Courage-Khazaka Corneometer, as well as the reliability of these devices, at a single institution. Two measurements per device were taken on the left volar forearm. Participants performed their own measurements with GPSkin while study personnel collected the remainder of data. Climate was controlled to 20-22 C and 30-50% humidity. Participants (n¼50) abstained from moisturizing and bathing for at least 6 hours prior to measurements. GPSkin and the AquaFlux demonstrated moderate correlation by Spearmans (r s ¼0.48, p¼0.0004). GPSkin and the Corneometer demonstrated moderately strong correlation (r s ¼0.63, p¼Additional analyses were performed removing measurements with a >4-fold difference in repeated values, all within the GPSkin TEWL measurements. Excluding these outliers (n¼42), GPSkin TEWL ICC improved to 0.54 (95% CI: 0.29-0.72) and correlated better with the AquaFlux (r s ¼ 0.52, p¼0.0004). Results from this study suggest a future role for this novel device in barrier studies or for patient-directed skin barrier measurement. Additional study of outlier data may identify strategies to optimize device reliability.
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