SPRR genes (formerly SPR) encode a novel class of polypeptides (small proline rich proteins) that are strongly induced during differentiation of human epidermal keratinocytes in vitro and in vivo. The most characteriztic feature of the SPRR gene family resides in the structure of the central segments of the encoded polypeptides that are built up from tandemly repeated units of either eight (SPRR1 and SPRR3) or nine (SPRR2) amino acids with the general consensus XKXPEPXX where X is any amino acid. In order to avoid bacterial contamination due to the high polar-nature of the HMM the threshold has been set very high.
Jiyao W et al.(2023). "The conserved domain database in 2023.",