title: Crystal structure and assembly of the functional Nanoarchaeum equitans tRNA splicing endonuclease.
abstract: The RNA splicing and processing endonuclease from Nanoarchaeum equitans (NEQ) belongs to the recently identified (alphabeta)(2) family of splicing endonucleases that require two different subunits for splicing activity. N. equitans splicing endonuclease comprises the catalytic subunit (NEQ205) and the structural subunit (NEQ261). Here, we report the crystal structure of the functional NEQ enzyme at 2.1 A containing both subunits, as well as that of the NEQ261 subunit alone at 2.2 A. The functional enzyme resembles previously known alpha(2) and alpha(4) endonucleases but forms a heterotetramer: a dimer of two heterodimers of the catalytic subunit (NEQ205) and the structural subunit (NEQ261). Surprisingly, NEQ261 alone forms a homodimer, similar to the previously known homodimer of the catalytic subunit. The homodimers of isolated subunits are inhibitory to heterodimerization as illustrated by a covalently linked catalytic homodimer that had no RNA cleavage activity upon mixing with the structural subunit. Detailed structural comparison reveals a more favorable hetero- than homodimerization interface, thereby suggesting a possible regulation mechanism of enzyme assembly through available subunits. Finally, the uniquely flexible active site of the NEQ endonuclease provides a possible explanation for its broader substrate specificity.
authors: Department of Chemistry and Biochemistry, Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA.
authors: Michelle
authors: M
authors: Mitchell
authors: Song
authors: S
authors: Xue
authors: Rachel
authors: R
authors: Erdman
authors: Lennart
authors: L
authors: Randau
authors: Dieter
authors: D
authors: Söll
authors: Hong
authors: H
authors: Li
mesh_terms: D000595:Amino Acid Sequence; D019843:Archaeal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D019281:Dimerization; D004722:Endoribonucleases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D046588:Nanoarchaeota / Q000201:enzymology*; D011487:Protein Conformation; D021122:Protein Subunits / Q000737:chemistry; D012326:RNA Splicing; D012343:RNA, Transfer / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
chemical_list: D019843:Archaeal Proteins; D021122:Protein Subunits; D012343:RNA, Transfer; D004722:Endoribonucleases; C051012:splicing endonuclease