title: Modular organization of inteins and C-terminal autocatalytic domains.
abstract: Analysis of the conserved sequence features of inteins (protein "introns") reveals that they are composed of three distinct modular domains. The N-terminal (N) and C-terminal (C) domains are predicted to perform different parts of the autocatalytic protein splicing reaction. An optional endonuclease domain (EN) is shown to correspond to different types of homing endonucleases in different inteins. The N domain contains motifs predicted to catalyze the first steps of protein splicing, leading to the cleavage of the intein N terminus from its protein host. Intein N domain motifs are also found in C-terminal autocatalytic domains (CADs) present in hedgehog and other protein families. Specific residues in the N domain of intein and CADs are proposed to form a charge relay system involved in cleaving their N-termini. The intein C domain is apparently unique to inteins and contains motifs that catalyze the final protein splicing steps: ligation of the intein flanks and cleavage of its C terminus to release the free intein and spliced host protein. All intein EN domains known thus far have dodecapeptide (DOD, LAGLI-DADG) type homing endonuclease motifs. This work identifies an EN domain with an HNH homing-endonuclease motif and two new small inteins with no EN domains. One of these small inteins might be inactive or a "pseudo intein." The results suggest a modular architecture for inteins, clarify their origin and relationship to other protein families, and extend recent experimental findings on the functional roles of intein N, C, and EN motifs.
authors.affiliation: Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA. pietro@sparky.fhcrc.org
authors.forename: S
authors.initials: S
authors.lastname: Pietrokovski
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites / Q000502:physiology; D002265:Carboxylic Ester Hydrolases / Q000737:chemistry; D002384:Catalysis; D027081:DNA Gyrase; D004250:DNA Topoisomerases, Type II; D015252:Deoxyribonucleases, Type II Site-Specific / Q000502:physiology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019154:Protein Splicing / Q000502:physiology*; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D016415:Sequence Alignment
chemical_list: D001426:Bacterial Proteins; D011506:Proteins; D029701:Saccharomyces cerevisiae Proteins; D002265:Carboxylic Ester Hydrolases; C019952:cutinase; C037725:SCEI protein, S cerevisiae; D015252:Deoxyribonucleases, Type II Site-Specific; D027081:DNA Gyrase; D004250:DNA Topoisomerases, Type II