This family includes the HABP4 family of hyaluronan-binding proteins, and the PAI-1 mRNA-binding protein, PAI-RBP1. HABP4 has been observed to bind hyaluronan (a glucosaminoglycan), but it is not known whether this is its primary role in vivo. It has also been observed to bind RNA, but with a lower affinity than that for hyaluronan [1]. PAI-1 mRNA-binding protein specifically binds the mRNA of type-1 plasminogen activator inhibitor (PAI-1), and is thought to be involved in regulation of mRNA stability [2]. However, in both cases, the sequence motifs predicted to be important for ligand binding are not conserved throughout the family, so it is not known whether members of this family share a common function.

1: Molecular characterization of a novel intracellular hyaluronan-binding protein. Huang L, Grammatikakis N, Yoneda M, Banerjee SD, Toole BP; J Biol Chem 2000;275:29829-29839. PMID:10887182

2: Identification and cDNA cloning of a novel RNA-binding protein that interacts with the cyclic nucleotide-responsive sequence in the Type-1 plasminogen activator inhibitor mRNA. Heaton JH, Dlakic WM, Dlakic M, Gelehrter TD; J Biol Chem 2001;276:3341-3347. PMID:11001948