InterPro: IPR004087 K Homology

The K homology (KH) domain was first identified in the human heterogeneous nuclear ribonucleoprotein (hnRNP) K. An evolutionarily conserved sequence of around 70 amino acids, the KH domain is present in a wide variety of nucleic acid-binding proteins. The KH domain binds RNA, and can function in RNA recognition [1]. It is found in multiple copies in several proteins, where they can function cooperatively or independently. For example, in the AU-rich element RNA-binding protein KSRP, which has 4 KH domains, KH domains 3 and 4 behave as independent binding modules to interact with different regions of the AU-rich RNA targets [1]. The solution structure of the first KH domain of FMR1 [2] and of the C-terminal KH domain of hnRNP K [3] determined by nuclear magnetic resonance (NMR) revealed a beta-alpha-alpha-beta-beta-alpha structure. Proteins containing KH domains include:

• Bacterial and organelle PNPases [4].
• Archaeal and eukaryotic exosome subunits [5].
• Eukaryotic and prokaryotic RS3 ribosomal proteins [6].
• Vertebrate fragile X mental retardation protein 1 (FMR1) [7].
• Vigilin, which has 14 KH domains [8].
• AU-rich element RNA-binding protein KSRP.
• hnRNP K, which contains 3 KH domains.
• Human onconeural ventral antigen-1 (NOVA-1) [9].

More information about these proteins can be found at Protein of the Month: RNA Exosomes [10].