Probing the Crystal Structure Landscape by Doping: 4-Bromo, 4-Chloro, and 4-Methylcinnamic Acids.

Accessing the data points in the crystal structure landscape of a molecule is a challenging task, either experimentally or computationally. We have charted the crystal structure landscape of 4-bromocinnamic acid (4BCA) experimentally and computationally: experimental doping is achieved with 4-methylcinnamic acid (4MCA) to obtain new crystal structures; computational doping is performed with 4-chlorocinnamic acid (4CCA) as a model system, because of the difficulties associated in parameterizing the Br atom. The landscape of 4CCA is explored experimentally in turn, also by doping it with 4MCA, and is found to bear a close resemblance to the landscape of 4BCA, justifying the ready miscibility of these two halogenated cinnamic acids to form solid solutions without any change in crystal structure. In effect, 4MCA, 4CCA and 4BCA form a commutable group of crystal structures, which may be realized experimentally or computationally, and constitute the landscape. Unlike the results obtained by Kitaigorodskii, all but two of the multiple solid solutions obtained in the methyl-doping experiments take structures that are different from the hitherto observed crystal forms of the parent compounds. Even granted that the latter might be inherently polymorphic, this unusual observation provokes the suggestion that solid solution formation may be used to probe the crystal structure landscape. The influence of π⋅⋅⋅π interactions, weak hydrogen bonds and halogen bonds in directing the formation of these new structures is also seen.

Mediator links epigenetic silencing of neuronal gene expression with x-linked mental retardation.

Mediator occupies a central role in RNA polymerase II transcription as a sensor, integrator, and processor of regulatory signals that converge on protein-coding gene promoters. Compared to its role in gene activation, little is known regarding the molecular mechanisms and biological implications of Mediator as a transducer of repressive signals. Here we describe a protein interaction network required for extraneuronal gene silencing comprising Mediator, G9a histone methyltransferase, and the RE1 silencing transcription factor (REST; also known as neuron restrictive silencer factor, NRSF). We show that the MED12 interface in Mediator links REST with G9a-dependent histone H3K9 dimethylation to suppress neuronal genes in nonneuronal cells. Notably, missense mutations in MED12 causing the X-linked mental retardation (XLMR) disorders FG syndrome and Lujan syndrome disrupt its REST corepressor function. These findings implicate Mediator in epigenetic restriction of neuronal gene expression to the nervous system and suggest a pathologic basis for MED12-associated XLMR involving impaired REST-dependent neuronal gene regulation.

A recurrent mutation in MED12 leading to R961W causes Opitz-Kaveggia syndrome.

Opitz-Kaveggia syndrome (also known as FG syndrome) is an X-linked disorder characterized by mental retardation, relative macrocephaly, hypotonia and constipation. We report here that the original family for whom the condition is named and five other families have a recurrent mutation (2881C>T, leading to R961W) in MED12 (also called TRAP230 or HOPA), a gene located at Xq13 that functions as a thyroid receptor-associated protein in the Mediator complex.

Crystal packing and melting temperatures of small oxalate esters: the role of C-H···O hydrogen bonding.

The simple dialkyl oxalates are generally liquids at room temperature except for dimethyl and di-tert-butyl oxalate which melt at 327 and 343 K. The crystal structures of diethyl, di-iso-propyl, di-n-butyl, di-tert-butyl and methyl ethyl oxalates were determined. The liquid esters were crystallized using the cryocrystallization technique. A comparison of the intermolecular interactions and packing features in these crystal structures was carried out. The crystal structure of dimethyl oxalate was redetermined at various temperatures. The other compounds were also studied at several temperatures in order to assess the attractive nature of the hydrogen bonds therein. A number of moderate to well defined C-H···O interactions account for the higher melting points of the two solid esters. Additionally, a diminished entropic contribution ΔS(m) in di-tert-butyl oxalate possibly increases the melting point of this compound further.

Sequencing of TGF-beta pathway genes in familial cases of intracranial aneurysm.

BACKGROUND AND PURPOSE: Familial aggregation of intracranial aneurysms (IA) strongly suggests a genetic contribution to pathogenesis. However, genetic risk factors have yet to be defined. For families affected by aortic aneurysms, specific gene variants have been identified, many affecting the receptors to transforming growth factor-beta (TGF-beta). In recent work, we found that aortic and intracranial aneurysms may share a common genetic basis in some families. We hypothesized, therefore, that mutations in TGF-beta receptors might also play a role in IA pathogenesis. METHODS: To identify genetic variants in TGF-beta and its receptors, TGFB1, TGFBR1, TGFBR2, ACVR1, TGFBR3, and ENG were directly sequenced in 44 unrelated patients with familial IA. Novel variants were confirmed by restriction digestion analyses, and allele frequencies were analyzed in cases versus individuals without known intracranial disease. Similarly, allele frequencies of a subset of known SNPs in each gene were also analyzed for association with IA. RESULTS: No mutations were found in TGFB1, TGFBR1, TGFBR2, or ACVR1. Novel variants identified in ENG (p.A60E) and TGFBR3 (p.W112R) were not detected in at least 892 reference chromosomes. ENG p.A60E showed significant association with familial IA in case-control studies (P=0.0080). No association with IA could be found for any of the known polymorphisms tested. CONCLUSIONS: Mutations in TGF-beta receptor genes are not a major cause of IA. However, we identified rare variants in ENG and TGFBR3 that may be important for IA pathogenesis in a subset of families.

The original Lujan syndrome family has a novel missense mutation (p.N1007S) in the MED12 gene.

A novel missense mutation in the mediator of RNA polymerase II transcription subunit 12 (MED12) gene has been found in the original family with Lujan syndrome and in a second family (K9359) that was initially considered to have Opitz-Kaveggia (FG) syndrome. A different missense mutation in the MED12 gene has been reported previously in the original family with FG syndrome and in five other families with compatible clinical findings. Neither sequence alteration has been found in over 1400 control X chromosomes. Lujan (Lujan-Fryns) syndrome is characterised by tall stature with asthenic habitus, macrocephaly, a tall narrow face, maxillary hypoplasia, a high narrow palate with dental crowding, a small or receding chin, long hands with hyperextensible digits, hypernasal speech, hypotonia, mild-to-moderate mental retardation, behavioural aberrations and dysgenesis of the corpus callosum. Although Lujan syndrome has not been previously considered to be in the differential diagnosis of FG syndrome, there are some overlapping clinical manifestations. Specifically, these are dysgenesis of the corpus callosum, macrocephaly/relative macrocephaly, a tall forehead, hypotonia, mental retardation and behavioural disturbances. Thus, it seems that these two X-linked mental retardation syndromes are allelic, with mutations in the MED12 gene.

Exploring the salt-cocrystal continuum with solid-state NMR using natural-abundance samples: implications for crystal engineering.

There has been significant recent interest in differentiating multicomponent solid forms, such as salts and cocrystals, and, where appropriate, in determining the position of the proton in the X-H⋯A-YX-⋯H-A+-Y continuum in these systems, owing to the direct relationship of this property to the clinical, regulatory and legal requirements for an active pharmaceutical ingredient (API). In the present study, solid forms of simple cocrystals/salts were investigated by high-field (700 MHz) solid-state NMR (ssNMR) using samples with naturally abundant 15N nuclei. Four model compounds in a series of prototypical salt/cocrystal/continuum systems exhibiting {PyN⋯H-O-}/{PyN+-H⋯O-} hydrogen bonds (Py is pyridine) were selected and prepared. The crystal structures were determined at both low and room temperature using X-ray diffraction. The H-atom positions were determined by measuring the 15N-1H distances through 15N-1H dipolar interactions using two-dimensional inversely proton-detected cross polarization with variable contact-time (invCP-VC) 1H→15N→1H experiments at ultrafast (νR ≥ 60-70 kHz) magic angle spinning (MAS) frequency. It is observed that this method is sensitive enough to determine the proton position even in a continuum where an ambiguity of terminology for the solid form often arises. This work, while carried out on simple systems, has implications in the pharmaceutical industry where the salt/cocrystal/continuum condition of APIs is considered seriously.

Succinate esters: odd-even effects in melting points.

Dialkyl succinates show a pattern of alternating behavior in their melting points, as the number of C atoms in the alkane side chain increases, unlike in the dialkyl oxalates [Joseph et al. (2011). Acta Cryst. B67, 525-534]. Dialkyl succinates with odd numbers of C atoms in the alkyl side chain show higher melting points than the immediately adjacent analogues with even numbers. The crystal structures and their molecular packing have been analyzed for a series of dialkyl succinates with 1-4 C atoms in the alkyl side chain. The energy difference (ΔE) between the optimized and observed molecular conformations, density, Kitaigorodskii packing index (KPI) and C-H...O interactions are considered to rationalize this behavior. In contrast to the dialkyl oxalates where a larger number of moderately strong C-H...O interactions were characteristic of oxalates with elevated melting points, here the molecular packing and the density play a major role in raising the melting point. On moving from oxalate to succinate esters the introduction of the C2 spacer adds two activated H atoms to the asymmetric unit, resulting in the formation of stronger C-H...O hydrogen bonds in all succinates. As a result the crystallinity of long-chain alkyl substituted esters improves enormously in the presence of hydrogen bonds from activated donors.

A novel mutation in type II methemoglobinemia.

Type II methemoglobinemia is a somatic deficiency of cytochrome b5 reductase with severe global neurologic impairment. We report a novel mutation in exon 3 of the CYB5R3 gene on chromosome 22 consisting of homozygous 1-base pair (bp) deletion noted as c.215delG; p.Gly72AlafsX100. The patient had improvement of gross motor skills, chewing, and swallowing that may be due to the initiation of daily ascorbic acid therapy. We hypothesize that a possible response to ascorbic acid may be related to the effect of making additional ferrous iron available for its role as a cofactor in carnitine synthesis.