1MI8: 2.0 Angstrom Crystal Structure Of A Dnab Intein From Synechocystis Sp. Pcc 6803

We have determined the crystal structure of a 154-residue intein derived from the dnaB gene of Synechocystis sp. strain PCC6803 and refined it to a 2.0-A resolution. The x-ray structure suggests that this intein possesses two catalytic sites that appear to be separately responsible for splicing and cleavage of the N- and C-terminal scissile bonds. The conserved intein block F residues are the important components of a catalytic site for side chain cyclization of the last intein residue, Asn-154. The data suggest that the imidazole ring of His-143 is involved in the activation of the side chain Ndelta atom of Asn-154, leading to a nucleophilic attack on the carbonyl carbon of Asn-154. Substitution of His-143 with Ala or Gln resulted in the inhibition of C-terminal cleavage. His-153, Asp-136, and a water molecule appear to constitute an oxyanion binding site by contacting the carbonyl oxygen of Asn-154 to stabilize the transition state. The structure and mutagenesis data also support that the close contact between the hydroxyl groups of Thr-138 and Ser-155, whose side chain participates in an S --> O acyl shift, plays an important role in the nucleophile orientation. Our structural modeling suggests that this catalytic module is conserved in the C-terminal subdomains of inteins from diverse organisms.
PDB ID: 1MI8Download
MMDB ID: 24075
PDB Deposition Date: 2002/8/22
Updated in MMDB: 2012/11
Experimental Method:
x-ray diffraction
Resolution: 2  Å
Source Organism:
Similar Structures:
Biological Unit for 1MI8: dimeric; determined by author
Molecular Components in 1MI8
Label Count Molecule
Proteins (2 molecules)
Dnab Intein
Molecule annotation
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