Solution NMR Studies of an Alternative Mode of Sin3 Engagement by the Sds3 Subunit in the Histone Deacetylase-Associated Sin3L/Rpd3L Corepressor Complex

Distinct biochemical properties of the class I histone deacetylase complexes

Classical histone deacetylases (HDACs) are enzymes that can hydrolytically cleave acetyl-Lys in histones and other proteins and serve as established drug targets in some forms of cancer. Class I HDACs 1-3 typically exist in a range of multiprotein complexes inside cells and show distinct biological functions in modulating gene expression. In recent years, it has become possible to purify and analyze the structure and enzymatic properties of several of these HDAC complexes, including CoREST, MiDAC, NuRD, Sin3, SMRT, MIER, and RERE. Here, we summarize what is experimentally established and/or computationally predicted about the structure of these complexes to describe their particular catalytic activities and site-specificities with modified nucleosome substrates.

Interactions, structural aspects, and evolutionary perspectives of the yeast 'START'-regulatory network

Molecular signal transduction networks which conduct transcription at the G1 to S phase transition of the eukaryotic cell division cycle have been identified in diverse taxa from mammals to baker´s yeast with analogous functional organization. However, regarding some network components, such as the transcriptional regulators STB1 and WHI5, only few orthologs exist which are confined to individual Saccharomycotina species. While Whi5 has been characterized as yeast analog of human Rb protein, in the particular case of Stb1 (Sin three binding protein 1) identification of functional analogs emerges as difficult because to date its exact functionality still remains obscured. By aiming to resolve Stb1´s enigmatic role this Perspectives article especially surveys works covering relations between Cyclin/CDKs, the heteromeric transcription factor complexes SBF (Swi4/Swi6) and MBF (Mbp1/Swi6), as well as additional coregulators (Whi5, Sin3, Rpd3, Nrm1) which are collectively associated with the orderly transcription at 'Start' of the Saccharomyces cerevisiae cell cycle. In this context, interaction capacities of the Sin3-scaffold protein are widely surveyed because its four PAH domains (Paired Amphiphatic Helix) represent a 'recruitment-code' for gene-specific targeting of repressive histone deacetylase activity (Rpd3) via different transcription factors. Here Stb1 plays a role in Sin3´s action on transcription at the G1/S-boundary. Through bioinformatic analyses a potential Sin3-interaction domain (SID) was detected in Stb1, and beyond that, connections within the G1/S-regulatory network are discussed in structural and evolutionary context thereby providing conceptual perspectives.

Integrative Modeling of a Sin3/HDAC Complex Sub-structure

Sin3/HDAC complexes function by deacetylating histones, condensing chromatin, and modulating gene expression. Although components used to build these complexes have been well defined, we still have only a limited understanding of the structure of the Sin3/HDAC subunits assembled around the scaffolding protein SIN3A. To characterize the spatial arrangement of Sin3 subunits, we combined Halo affinity capture, chemical crosslinking, and high-resolution mass spectrometry (XL-MS) to determine intersubunit distance constraints, identifying 66 interprotein and 63 self-crosslinks for 13 Sin3 subunits. Having assessed crosslink authenticity by mapping self-crosslinks onto existing structures, we used distance restraints from interprotein crosslinks to guide assembly of a Sin3 complex substructure. We identified the relative positions of subunits SAP30L, HDAC1, SUDS3, HDAC2, and ING1 around the SIN3A scaffold. The architecture of this subassembly suggests that multiple factors have space to assemble to collectively influence the behavior of the catalytic subunit HDAC1.

Banks et al. capture positional information for subunits within Sin3/HDAC complexes by combining crosslinking and high-resolution mass spectrometry. This information is then used to guide docking of Sin3 subunit structures to develop a model of a Sin3/HDAC complex sub-structure.

Identification of Topological Network Modules in Perturbed Protein Interaction Networks

Biological networks consist of functional modules, however detecting and characterizing such modules in networks remains challenging. Perturbing networks is one strategy for identifying modules. Here we used an advanced mathematical approach named topological data analysis (TDA) to interrogate two perturbed networks. In one, we disrupted the S. cerevisiae INO80 protein interaction network by isolating complexes after protein complex components were deleted from the genome. In the second, we reanalyzed previously published data demonstrating the disruption of the human Sin3 network with a histone deacetylase inhibitor. Here we show that disrupted networks contained topological network modules (TNMs) with shared properties that mapped onto distinct locations in networks. We define TMNs as proteins that occupy close network positions depending on their coordinates in a topological space. TNMs provide new insight into networks by capturing proteins from different categories including proteins within a complex, proteins with shared biological functions, and proteins disrupted across networks.