Characterisation of an Ovine Keratin Associated Protein (KAP) Gene, Which Would Produce a Protein Rich in Glycine and Tyrosine, but Lacking in Cysteine

Abstract

The keratin-associated proteins (KAPs) are structural components of hair/wool fibres. All of the KAPs identified to date contain cysteine, which is thought to form disulphide bonds cross-linking the keratin intermediate filaments. Here, we report the identification of a KAP gene in sheep that would produce a protein that contains a high proportion (63.2 mol%) of glycine and tyrosine, but would not contain any cysteine. This suggests that other forms of intra- and inter-strand interaction may occur with this KAP, such as interactions via ring-stacking and hydrogen-bonding. The gene was dissimilar to any previously reported KAP gene, and was therefore assigned to a new family, and named KRTAP36-1. The KRTAP36-1 genome sequence was almost identical to some EST sequences from sheep and goat skin follicles, suggesting that it is present and expressed in sheep and goats. A BLAST search of the human genome assembly sequence did not reveal any human homologue. Three variant sequences (named A to C) of ovine KRTAP36-1 were identified and four single nucleotide polymorphisms (SNPs) were detected. One SNP was located 32 bp upstream of the coding region, and all of the others were in the coding region and were nonsynonymous. After correcting for potential linkage to the proximal KRTAP20-1, variant B of KRTAP36-1 was found to be associated with increased prickle factor (PF) in wool, suggesting that variation in the gene may have the potential to be used as gene marker for breeding sheep with lower PF.

Keywords: Keratin-associated protein KAP36-1 gene (KRTAP36-1); prickle factor; sheep; variation; wool traits.

Figure 1

KRTAPs identified on the sheep chromosome 1 region that contains a newly identified KRTAP36-1. The newly identified gene is shown in a box, and the 17 previously identified KRTAPs are also shown. Vertical bars represent the location of different KRTAPs and the arrowheads indicate the direction of transcription. The numbers below the bars indicate the name of the respective KAP genes (i.e., 11.1 is KRTAP11-1). The nucleotide distances are approximately and refer to NC_019458.2.

Figure 2

Phylogenetic tree of the HGT-KAPs identified in sheep and human. The tree was constructed using the predicted amino acid sequences. The numbers at the forks indicate the bootstrap confidence values and only those equal to or higher than 50% are shown. The sheep KAPs are indicated with a prefix “s”, whereas the human sequences are indicated with “h”. The newly identified ORF is designated as sheep KAP36-1 gene and is indicated in box. The GenBank accession numbers for other sheep HGT-KAPs are NM_001193399 (sKAP6-1), KT725832 (sKAP6-2), KT725837 (sKAP6-3), KT725840 (sKAP6-4), KT725845 (sKAP6-5), X05638 (sKAP7-1), X05639 (sKAP8-1), KF220646 (sKAP8-2), MH243552 (sKAP20-1), MH071391 (sKAP20-2) and KX377616 (sKAP22-1). The GenBank accession numbers for human HGT-KAPs are: NM_181602 (hKAP6-1), NM_181604 (hKAP6-2), NM_181605 (hKAP6-3), AJ457063 (hKAP7-1), AJ457064 (hKAP8-1), AJ457067 (hKAP19-1), NM_181608 (hKAP19-2), NM_181609 (hKAP19-3), NM_181610 (hKAP19-4), NM_181611 (hKAP19-5), NM_181612 (hKAP19-6), NM_181614 (hKAP19-7), NM_181615 (hKAP20-1), NM_181616 (hKAP20-2), NM_181619 (hKAP21-1), NM_181617 (hKAP21-2) and NM_181620 (hKAP22-1).

Figure 3

Polymorphism of ovine KRTAP36-1. (a) Three variants (A to C) in either homozygous or heterozygous forms were detected by PCR-SSCP. (b) Four single nucleotide polymorphisms (SNPs) were found in these variants. (c) Three of the SNPs would lead to amino acid changes and result in three different amino acid sequences.