Aurora-B is a component of the Chromosomal Passenger Complex (CPC) required for correct spindle-kinetochore attachments during chromosome segregation and for cytokinesis. The chromatin factors that recruit the CPC to centromeres are unknown, however. Here we show that phosphorylation of Histone-H3 Thr-3 (H3T3ph) by Haspin is necessary for CPC accumulation at centromeres, and that the CPC subunit Survivin binds directly to H3T3ph. A non-binding Survivin-D70A/D71A mutant does not support centromeric CPC concentration and both Haspin depletion and Survivin-D70A/D71A mutation diminish centromere localization of MCAK and mitotic checkpoint signaling in taxol. Survivin-D70A/D71A mutation and microinjection of H3T3ph-specific antibody both compromise centromeric Aurora-B functions but do not prevent cytokinesis. Therefore, H3T3ph generated by Haspin positions the CPC at centromeres to regulate selected targets of Aurora-B during mitosis.

Survivin, a subunit of the chromosome passenger complex (CPC), binds the N-terminal tail of histone H3, which is phosphorylated on T3 by Haspin kinase, and localizes the complex to the inner centromeres. We used x-ray crystallography to determine the residues of Survivin that are important in binding phosphomodified histone H3. Mutation of amino acids that interact with the histone N-terminus lowered in vitro tail binding affinity and reduced CPC recruitment to the inner centromere in cells, validating our solved structures. Phylogenetic analysis shows that nonmammalian vertebrates have two Survivin paralogues, which we name class A and B. A distinguishing feature of these paralogues is an H-to-R change in an amino acid that interacts with the histone T3 phosphate. The binding to histone tails of the human class A paralogue, which has a histidine at this position, is sensitive to changes around physiological pH, whereas Xenopus Survivin class B is less so. Our data demonstrate that Survivin paralogues have different characteristics of phosphospecific binding to threonine-3 of histone H3, providing new insight into the biology of the inner centromere.

Metals have crucial roles in many physiological, pathological, toxicological, pharmaceutical, and diagnostic processes. Proper handling of metal-containing macromolecule samples for structural studies is not trivial, and failure to handle them properly is often a source of irreproducibility caused by issues such as pH changes, incorporation of unexpected metals, or oxidization/reduction of the metal. This protocol outlines the guidelines and best practices for characterizing metal-binding sites in protein structures and alerts experimenters to potential pitfalls during the preparation and handling of metal-containing protein samples for X-ray crystallography studies. The protocol features strategies for controlling the sample pH and the metal oxidation state, recording X-ray fluorescence (XRF) spectra, and collecting diffraction data sets above and below the corresponding metal absorption edges. This protocol should allow experimenters to gather sufficient evidence to unambiguously determine the identity and location of the metal of interest, as well as to accurately characterize the coordinating ligands in the metal binding environment within the protein. Meticulous handling of metal-containing macromolecule samples as described in this protocol should enhance experimental reproducibility in biomedical sciences, especially in X-ray macromolecular crystallography. For most samples, the protocol can be completed within a period of 7-190 d, most of which (2-180 d) is devoted to growing the crystal. The protocol should be readily understandable to structural biologists, particularly protein crystallographers with an intermediate level of experience.