ABSTRACT
The successful assembly and regulation of the kinetochore are critical for the equal and accurate segregation of genetic material during the cell cycle. CENP-C (centromere protein C), a conserved inner kinetochore component, has been broadly characterized as a scaffolding protein and is required for the recruitment of multiple kinetochore proteins to the centromere. At its C terminus, CENP-C harbors a conserved cupin domain that has an established role in protein dimerization. Although the crystal structure of the Saccharomyces cerevisiae Mif2CENP-C cupin domain has been determined, centromeric organization and kinetochore composition vary greatly between S. cerevisiae (point centromere) and other eukaryotes (regional centromere). Therefore, whether the structural and functional role of the cupin domain is conserved throughout evolution requires investigation. Here, we report the crystal structures of the Schizosaccharomyces pombe and Drosophila melanogaster CENP-C cupin domains at 2.52 and 1.81 Å resolutions, respectively. Although the central jelly roll architecture is conserved among the three determined CENP-C cupin domain structures, the cupin domains from organisms with regional centromeres contain additional structural features that aid in dimerization. Moreover, we found that the S. pombe Cnp3CENP-C jelly roll fold harbors an inner binding pocket that is used to recruit the meiosis-specific protein Moa1. In summary, our results unveil the evolutionarily conserved and unique features of the CENP-C cupin domain and uncover the mechanism by which it functions as a recruitment factor.
Subject(s)
Chromosomal Proteins, Non-Histone/metabolism , Chromosomal Proteins, Non-Histone/ultrastructure , Animals , Cell Cycle Proteins/metabolism , Centromere/metabolism , Centromere Protein A/metabolism , Crystallography, X-Ray/methods , DNA-Binding Proteins/metabolism , Dimerization , Drosophila Proteins/metabolism , Drosophila Proteins/ultrastructure , Drosophila melanogaster/metabolism , Histones/metabolism , Kinetochores/metabolism , Kinetochores/ultrastructure , Schizosaccharomyces/metabolism , Schizosaccharomyces pombe Proteins/metabolismABSTRACT
The Mis18 complex, composed of Mis16, Eic1, and Mis18 in fission yeast, selectively deposits the centromere-specific histone H3 variant, CENP-ACnp1, at centromeres. How the intact Mis18 holo-complex oligomerizes and how Mis16, a well-known ubiquitous histone H4 chaperone, plays a centromere-specific role in the Mis18 holo-complex, remain unclear. Here, we report the stoichiometry of the intact Mis18 holo-complex as (Mis16)2:(Eic1)2:(Mis18)4 using analytical ultracentrifugation. We further determine the crystal structure of Schizosaccharomyces pombe Mis16 in complex with the C-terminal portion of Eic1 (Eic1-CT). Notably, Mis16 accommodates Eic1-CT through the binding pocket normally occupied by histone H4, indicating that Eic1 and H4 compete for the same binding site, providing a mechanism for Mis16 to switch its binding partner from histone H4 to Eic1. Thus, our analyses not only determine the stoichiometry of the intact Mis18 holo-complex but also uncover the molecular mechanism by which Mis16 plays a centromere-specific role through Eic1 association.
Subject(s)
Carrier Proteins/metabolism , Multiprotein Complexes/metabolism , Schizosaccharomyces pombe Proteins/metabolism , Schizosaccharomyces/metabolism , Carrier Proteins/chemistry , Chromosomal Proteins, Non-Histone/metabolism , Crystallography, X-Ray , Histones/metabolism , Models, Molecular , Multiprotein Complexes/chemistry , Protein Multimerization , Schizosaccharomyces/chemistry , Schizosaccharomyces pombe Proteins/chemistryABSTRACT
LAGLIDADG meganucleases are DNA cleaving enzymes used for genome engineering. While their cleavage specificity can be altered using several protein engineering and selection strategies, their overall targetability is limited by highly specific indirect recognition of the central four base pairs within their recognition sites. In order to examine the physical basis of indirect sequence recognition and to expand the number of such nucleases available for genome engineering, we have determined the target sites, DNA-bound structures, and central four cleavage fidelities of nine related enzymes. Subsequent crystallographic analyses of a meganuclease bound to two noncleavable target sites, each containing a single inactivating base pair substitution at its center, indicates that a localized slip of the mutated base pair causes a small change in the DNA backbone conformation that results in a loss of metal occupancy at one binding site, eliminating cleavage activity.
