Proteomic analysis of human nail plate

Abstract

Shotgun proteomic analysis of the human nail plate identified 144 proteins in samples from Causcasian volunteers. The 30 identified proteins solubilized by detergent and reducing agent, 90% of the total nail plate mass, were primarily keratins and keratin associated proteins. Keratins comprised a majority of the detergent-insoluble fraction as well, but numerous cytoplasmic, membrane, and junctional proteins and histones were also identified, indicating broad use by transglutaminases of available proteins as substrates for cross-linking. Two novel membrane proteins were identified, also found in the hair shaft, for which mRNAs were detected only at very low levels by real-time polymerase chain reaction in other tissues. Parallel analyses of nail samples from volunteers from Inner Mongolia, China gave essentially the same protein profiles. Comparison of the profiles of nail plate and hair shaft from the latter volunteers revealed extensive overlap of protein constituents. Analyses of samples from an arsenic-exposed population revealed few proteins whose levels were altered substantially but raised the possibility of detecting sensitive individuals in this way.

Figure 1

Comparison of yields obtained from the solubilized versus insoluble fractions from nail plate. The 50 proteins with the highest number of unique peptides are grouped as cytoskeletal (keratins and keratin associated proteins) and membrane and intracellular proteins (the remainder). Illustrated are means and standard deviations of 4 samples.

Figure 2

Comparison of yields obtained from the solubilized versus insoluble fractions from hair shaft. The 50 proteins with the highest number of unique peptides are grouped as cytoskeletal (keratins and keratin associated proteins) and membrane and intracellular proteins (the remainder). Illustrated are means and standard deviations of 4 samples.

Figure 3

Overlapping protein expression in nail plate and hair shaft. The numbers of unique peptides, means and standard deviations of four independent samples, obtained for the particulate fraction remaining after extensive detergent extraction are illustrated for (a) junctional and membrane proteins, (b) keratins and keratin associated proteins and (c) the remaining cellular proteins. The 50 proteins with the highest number of unique peptides from hair and from nail samples are merged and illustrated in order of decreasing unique peptides for the nail samples.