David Neuhaus

The structural basis for the recognition of acetylated histone H4 by the bromodomain of histone acetyltransferase Gcn5p

The bromodomain is an ∼110 amino acid module found in histone acetyltransferases and the ATPase component of certain nucleosome remodelling complexes. We report the crystal structure at 1.9 Å resolution of the Saccharomyces cerevisiae Gcn5p bromodomain complexed with a peptide corresponding to residues 15–29 of histone H4 acetylated at the ζ‐N of lysine 16. We show that this bromodomain preferentially binds to peptides containing an N‐acetyl lysine residue. Only residues 16–19 of the acetylated peptide interact with the bromodomain. The primary interaction is the N‐acetyl lysine binding in a cleft with the specificity provided by the interaction of the amide nitrogen of a conserved asparagine with the oxygen of the acetyl carbonyl group. A network of water‐mediated H‐bonds with protein main chain carbonyl groups at the base of the cleft contributes to the binding. Additional side chain binding occurs on a shallow depression that is hydrophobic at one end and can accommodate charge interactions at the other. These findings suggest that the Gcn5p bromodomain may discriminate between different acetylated lysine residues depending on the context in which they are displayed.

Structure of a soluble, glycosylated form of the human complement regulatory protein CD59

BACKGROUND CD59 is a cell-surface glycoprotein that protects host cells from complement-mediated lysis by binding to and preventing the normal functioning of the complement proteins C8 and/or C9 which form part of a membrane penetrating assembly called the membrane attack complex. CD59 has no structural similarity to other complement proteins, but is an example of a plasma protein domain type found also in murine Ly-6 proteins and the urokinase-type plasminogen activator receptor. RESULTS CD59 was purified from human urine, retaining the N-glycan and at least some of the non-lipid component of the glycosylphosphatidylinositol membrane anchor. The three-dimensional structure of the protein component has been determined in the presence of the carbohydrate groups using two-dimensional NMR spectroscopy. The protein structure is well defined by the NMR data (root mean square deviation from the mean structure of 0.65 A for backbone atoms and no distance constraint violations greater than 0.4 A). Structure calculations were also carried out to model the orientation of the N-acetylglucosamine residue that is directly linked to Asn18. CONCLUSIONS The main features of the protein structure are two antiparallel beta-sheets (a central one with three strands and another with two), a short helix that packs against the three-stranded beta-sheet, and a carboxy-terminal region that, although lacking regular secondary structure, is well defined and packs against the three-stranded beta-sheet, on the opposite face to the helix. We have used the structure, in combination with existing biochemical data, to identify residues that may be involved in C8 binding.

Structural basis of the RNA-binding specificity of human U1A protein.

The RNP domain is a very common eukaryotic protein domain involved in recognition of a wide range of RNA structures and sequences. Two structures of human U1A in complex with distinct RNA substrates have revealed important aspects of RNP‐RNA recognition, but have also raised intriguing questions concerning the origin of binding specificity. The β‐sheet of the domain provides an extensive RNA‐binding platform for packing aromatic RNA bases and hydrophobic protein side chains. However, many interactions between functional groups on the single‐stranded nucleotides and residues on the β‐sheet surface are potentially common to RNP proteins with diverse specificity and therefore make only limited contribution to molecular discrimination. The refined structure of the U1A complex with the RNA polyadenylation inhibition element reported here clarifies the role of the RNP domain principal specificity determinants (the variable loops) in molecular recognition. The most variable region of RNP proteins, loop 3, plays a crucial role in defining the global geometry of the intermolecular interface. Electrostatic interactions with the RNA phosphodiester backbone involve protein side chains that are unique to U1A and are likely to be important for discrimination. This analysis provides a novel picture of RNA‐protein recognition, much closer to our current understanding of protein‐protein recognition than that of DNA‐protein recognition.

The NMR structure of the 38 kDa U1A protein - PIE RNA complex reveals the basis of cooperativity in regulation of polyadenylation by human U1A protein.

The status of the poly(A) tail at the 3′-end of mRNAs controls the expression of numerous genes in response to developmental and extracellular signals. Poly(A) tail regulation requires cooperative binding of two human U1A proteins to an RNA regulatory region called the polyadenylation inhibition element (PIE). When bound to PIE RNA, U1A proteins also bind to the enzyme responsible for formation of the mature 3′-end of most eukaryotic mRNAs, poly(A) polymerase (PAP). The NMR structure of the 38 kDa complex formed between two U1A molecules and PIE RNA shows that binding cooperativity depends on helix C located at the end of the RNA-binding domain and just adjacent to the PAP-interacting domain of U1A. Since helix C undergoes a conformational change upon RNA binding, the structure shows that binding cooperativity and interactions with PAP occur only when U1A is bound to its cognate RNA. This mechanism ensures that the activity of PAP enzyme, which is essential to the cell, is only down regulated when U1A is bound to the U1A mRNA.

Treatment of NOE constraints involving equivalent or nonstereoassigned protons in calculations of biomacromolecular structures

SummaryTwo modifications to the commonly used protocols for calculating NMR structures are developed, relating to the treatment of NOE constraints involving groups of equivalent protons or nonstereoassigned diastereotopic protons. Firstly, a modified method is investigated for correcting for multiplicity, which is applicable whenever all NOE intensities are calibrated as a single set and categorised in broad intensity ranges. Secondly, a new set of values for ‘pseudoatom corrections’ is proposed for use with calculations employing ‘centre-averaging’. The effect of these protocols on structure calculations is demonstrated using two proteins, one of which is well defined by the NOE data, the other less so. It is shown that failure to correct for multiplicity when using ‘r-6 averaging’ results in overly precise structures, higher NOE energies and deviations from geometric ideality, while failure to correct for multiplicity when using ‘r-6 summation’ can cause an avoidable degradation of precision if the NOE data are sparse. Conversely, when multiplicities are treated correctly, r-6 averaging, r-6 summation and centre averaging all give closely comparable results when the structure is well defined by the data. When the NOE data contain less information, r-6 averaging or r-6 summation offer a significant advantage over centre averaging, both in terms of precision and in terms of the proportion of calculations that converge on a consisten result.

Structural consequences of disease-causing mutations in the ATRX-DNMT3-DNMT3L (ADD) domain of the chromatin-associated protein ATRX.

The chromatin-associated protein ATRX was originally identified because mutations in the ATRX gene cause a severe form of syndromal X-linked mental retardation associated with α-thalassemia. Half of all of the disease-associated missense mutations cluster in a cysteine-rich region in the N terminus of ATRX. This region was named the ATRX-DNMT3-DNMT3L (ADD) domain, based on sequence homology with a family of DNA methyltransferases. Here, we report the solution structure of the ADD domain of ATRX, which consists of an N-terminal GATA-like zinc finger, a plant homeodomain finger, and a long C-terminal α-helix that pack together to form a single globular domain. Interestingly, the α-helix of the GATA-like finger is exposed and highly basic, suggesting a DNA-binding function for ATRX. The disease-causing mutations fall into two groups: the majority affect buried residues and hence affect the structural integrity of the ADD domain; another group affects a cluster of surface residues, and these are likely to perturb a potential protein interaction site. The effects of individual point mutations on the folding state and stability of the ADD domain correlate well with the levels of mutant ATRX protein in patients, providing insights into the molecular pathophysiology of ATR-X syndrome.

DNA recognition by the oestrogen receptor: from solution to the crystal.

BACKGROUND The steroid/nuclear hormone receptors are a large family of conserved ligand-activated transcription factors that regulate gene expression through binding to response elements upstream of their target genes. Most members of this family bind to DNA as homodimers or heterodimers and recognize the sequence, spacing and orientation of the two half-sites of their response elements. The recognition and discrimination of the sequence and arrangements of these half-sites are mediated primarily by a highly conserved DNA-binding domain. RESULTS Here we describe the DNA-binding properties of the isolated DNA-binding domain of the oestrogen receptor, the ERDBD, and its refined NMR structure. This domain is monomeric in solution, but two molecules bind cooperatively to specific DNA sequences; this cooperativity determines the arrangement of half-sites that is recognized by the ERDBD. The 10 carboxy-terminal residues and a region of 15 residues within the domain are disordered in the solution structure, yet are important for DNA binding. CONCLUSION The cooperative nature of ERDBD binding to DNA is important. The previously-determined X-ray structure of the ERDBD dimer bound to DNA shows that the 15 internal residues disordered in solution make contact both with DNA and with the corresponding region of the other monomer. These results suggest that these residues become ordered during the process of binding to DNA, forming the dimer interface and thus contributing to the cooperative interaction between monomers.

Structural Basis for the Assembly of the Smrt/Ncor Core Transcriptional Repression Machinery.

Eukaryotic transcriptional repressors function by recruiting large coregulatory complexes that target histone deacetylase enzymes to gene promoters and enhancers. Transcriptional repression complexes, assembled by the corepressor NCoR and its homolog SMRT, are crucial in many processes, including development and metabolic physiology. The core repression complex involves the recruitment of three proteins, HDAC3, GPS2 and TBL1, to a highly conserved repression domain within SMRT and NCoR. We have used structural and functional approaches to gain insight into the architecture and biological role of this complex. We report the crystal structure of the tetrameric oligomerization domain of TBL1, which interacts with both SMRT and GPS2, and the NMR structure of the interface complex between GPS2 and SMRT. These structures, together with computational docking, mutagenesis and functional assays, reveal the assembly mechanism and stoichiometry of the corepressor complex.

Two-dimensional 1H nuclear magnetic resonance study of the (5–55) single-disulphide folding intermediate of bovine pancreatic trypsin inhibitor

An analogue of the bovine pancreatic trypsin inhibitor (BPTI) folding intermediate that contains only the disulphide bond between Cys5 and Cys55 has been prepared in Escherichia coli by protein engineering methods, with the other four Cys residues replaced by Ser. Two-dimensional 1H nuclear magnetic resonance studies of the analogue have resulted in essentially complete resonance assignments of the folded form of the protein. The folded protein has a compact conformation that is structurally very similar to that of native BPTI, although there are subtle differences and the folded conformation is not very stable. Approximately half of the protein molecules are unfolded at 3 degrees C, and this proportion increases at higher temperatures. The folded and unfolded conformations are in slow exchange. The conformational properties of the analogue can explain many aspects of the kinetic role that the normal (5-55) intermediate plays in the folding of BPTI.

Solution structures of the two PBZ domains from human APLF and their interaction with poly(ADP-ribose)

Addition of poly(ADP-ribose) (PAR) is an important post-translational modification in higher eukaryotes. Several DNA repair and checkpoint proteins possess specific PAR-binding zinc-finger (PBZ) modules critical for function. Here, we present solution structures of the two PBZ modules of aprataxin and PNK–like factor (APLF), revealing a novel type of zinc finger. By combining in vivo PAR-binding data with NMR interaction data using PAR fragments, we propose a structural basis for PBZ-PAR recognition.