A Transketolase Assembly Defect in a Wernicke-Korsakoff Syndrome Patient

Review of thiamine deficiency disorders: Wernicke encephalopathy and Korsakoff psychosis

Wernicke encephalopathy (WE) and Korsakoff psychosis (KP), together termed Wernicke-Korsakoff syndrome (WKS), are distinct yet overlapping neuropsychiatric disorders associated with thiamine deficiency. Thiamine pyrophosphate, the biologically active form of thiamine, is essential for multiple biochemical pathways involved in carbohydrate utilization. Both genetic susceptibilities and acquired deficiencies as a result of alcoholic and non-alcoholic factors are associated with thiamine deficiency or its impaired utilization. WKS is underdiagnosed because of the inconsistent clinical presentation and overlapping of symptoms with other neurological conditions. The identification and individualized treatment of WE based on the etiology is vital to prevent the development of the amnestic state associated with KP in genetically predisposed individuals. Through this review, we bring together the existing data from animal and human models to expound the etiopathogenesis, diagnosis, and therapeutic interventions for WE and KP.

Orchestration of thiamin biosynthesis and central metabolism by combined action of the thiamin pyrophosphate riboswitch and the circadian clock in Arabidopsis

Riboswitches are natural RNA elements that posttranscriptionally regulate gene expression by binding small molecules and thereby autonomously control intracellular levels of these metabolites. Although riboswitch-based mechanisms have been examined extensively, the integration of their activity with global physiology and metabolism has been largely overlooked. Here, we explored the regulation of thiamin biosynthesis and the consequences of thiamin pyrophosphate riboswitch deficiency on metabolism in Arabidopsis thaliana. Our results show that thiamin biosynthesis is largely regulated by the circadian clock via the activity of the THIAMIN C SYNTHASE (THIC) promoter, while the riboswitch located at the 3' untranslated region of this gene controls overall thiamin biosynthesis. Surprisingly, the results also indicate that the rate of thiamin biosynthesis directs the activity of thiamin-requiring enzymes and consecutively determines the rate of carbohydrate oxidation via the tricarboxylic acid cycle and pentose-phosphate pathway. Our model suggests that in Arabidopsis, the THIC promoter and the thiamin-pyrophosphate riboswitch act simultaneously to tightly regulate thiamin biosynthesis in a circadian manner and consequently sense and control vital points of core cellular metabolism.

[Wernicke's encephalopathy in non-alcoholic patients: a series of 8 cases]

INTRODUCTION

Wernicke's encephalopathy (WE) is an underdiagnosed condition, usually associated with alcoholism, and has a worse prognosis if there is a delay in diagnosis. A series of 8 non-alcoholic patients with WE is presented and an assessment is made on whether a delay in diagnosis leads to a worse prognosis.

PATIENTS AND METHODS

The clinical records of patients admitted to 2 university hospitals between 2004 and 2009 with the diagnosis of WE, excluding those with a history of alcoholism, were retrospectively reviewed.

RESULTS

The study included 4 men and 4 women aged 35-82 of whom 7 had a history of gastrointestinal pathology, and persistent vomiting was the precipitating factor in 7. Encephalopathy was the most frequent onset symptom (4). The classical triad was present in seven patients. Thiamine levels were low in 3/6 and normal in 3/6 cases. MRI was abnormal in seven patients, with high signal intensity in the diencephalon and mammillary bodies (7), periaqueductal grey matter (6), cortex (3) and cerebellum (1). Seven improved with thiamine. Sequelae were mild in 6, and severe in 2 after 6-12 months of follow-up. All patients with a diagnostic delay less than 18 days had mild sequelae.

CONCLUSIONS

Non-alcoholic WE frequently occurs after gastrointestinal disturbances that could result in lower thiamine absorption. Whereas thiamine levels can be normal in many cases, in almost all cases the MRI shows signal alterations in typical locations. A delay in the diagnosis, and therefore, in treatment leads to a worse prognosis.

The Thiamine diphosphate dependent Enzyme Engineering Database: a tool for the systematic analysis of sequence and structure relations

BACKGROUND

Thiamine diphosphate (ThDP)-dependent enzymes form a vast and diverse class of proteins, catalyzing a wide variety of enzymatic reactions including the formation or cleavage of carbon-sulfur, carbon-oxygen, carbon-nitrogen, and especially carbon-carbon bonds. Although very diverse in sequence and domain organisation, they share two common protein domains, the pyrophosphate (PP) and the pyrimidine (PYR) domain. For the comprehensive and systematic comparison of protein sequences and structures the Thiamine diphosphate (ThDP)-dependent Enzyme Engineering Database (TEED) was established.

DESCRIPTION

The TEED http://www.teed.uni-stuttgart.de contains 12048 sequence entries which were assigned to 9443 different proteins and 379 structure entries. Proteins were assigned to 8 different superfamilies and 63 homologous protein families. For each family, the TEED offers multisequence alignments, phylogenetic trees, and family-specific HMM profiles. The conserved pyrophosphate (PP) and pyrimidine (PYR) domains have been annotated, which allows the analysis of sequence similarities for a broad variety of proteins. Human ThDP-dependent enzymes are known to be involved in many diseases. 20 different proteins and over 40 single nucleotide polymorphisms (SNPs) of human ThDP-dependent enzymes were identified in the TEED.

CONCLUSIONS

The online accessible version of the TEED has been designed to serve as a navigation and analysis tool for the large and diverse family of ThDP-dependent enzymes.

A theoretical argument for inherited thiamine insensitivity as one possible biological cause of familial alcoholism

Thiamine deficiency has been specifically linked to the development of Wernicke-Korsakoff syndrome (WK)--a degenerative brain disorder that is typically associated with alcoholic drinking. Alcoholism-related thiamine deficiency is a major cause of WK. However, an inherited abnormality in thiamine utilization has been identified in some WK patients that may predispose heavy drinkers to this severe neurological syndrome. Individuals who possess this variant require more thiamine throughout their lives to prevent them from experiencing thiamine deficiency. Recent prospective studies have implicated early childhood nutritional and environmental influences in the etiology of alcoholism in adults. These studies have suggested that developmental abnormalities involving brain white matter growth might precipitate the later development of alcoholism possibly by altering the emerging reward-related brain systems. Brain white matter growth is highly sensitive to nutritional deficiency (including thiamine deficiency) and oxidative injury, especially during the perinatal period. The proposed model of familial alcoholism hypothesizes that an inherited insensitivity to thiamine can precipitate brain abnormalities very early in life that will greatly increase the risk of developing alcoholism in adulthood. This paper offers a heuristic model of a possible mechanism by which both inherited and environmental factors related to thiamine utilization might coaggregate to cause alcoholism.

Differential protein expression in the prefrontal white matter of human alcoholics: a proteomics study

Neuroimaging and post-mortem studies indicate that chronic alcohol use induces global changes in brain morphology, such as cortical and subcortical atrophy. Recent studies have shown that frontal lobe structures are specifically susceptible to alcohol-related brain damage and shrinkage in this area is largely due to a loss of white matter. This may explain the high incidence of cognitive dysfunction observed in alcoholics. Using a proteomics-based approach, changes in protein expression in the dorsolateral prefrontal region (BA9) white matter were identified in human alcoholic brains. Protein extracts from the BA9 white matter of 25 human brains (10 controls; eight uncomplicated alcoholics; six alcoholics complicated with hepatic cirrhosis; one reformed alcoholic) were separated using two-dimensional gel electrophoresis. Overall, changes in the relative expression of 60 proteins were identified (P<0.05, ANOVA) in the alcoholic BA9 white matter. In total, 18 protein spots have been identified using MALDI-TOF; including hNP22, alpha-internexin, transketolase, creatine kinase chain B, ubiquitin carboxy-terminal hydrolase L1 and glyceraldehyde-3-phosphate dehydrogenase. Several of these proteins have been previously implicated in alcohol-related disorders and brain damage. By identifying changes in protein expression in this region from alcoholics, hypotheses may draw upon more mechanistic explanations as to how chronic ethanol consumption causes white matter damage.

The role of cysteine 160 in thiamine diphosphate binding of the Calvin–Benson–Bassham cycle transketolase of Rhodobacter sphaeroides

The transketolase gene (cbbT) that encodes the Calvin-Benson-Bassham pathway transketolase (CbbT) of Rhodobacter sphaeroides was overexpressed in Escherichia coli and the recombinant protein purified to homogeneity. Like other transketolases, R. sphaeroides CbbT was found to be inactivated in the presence of oxygen. At its optimal pH of 7.8, CbbT displays a specific activity of 37 U/mg, a KR5P of 949 microM, a KXu5P of 11 microM, and a KThDP of 1.8 microM. Cysteine 160, equivalent to Cys159 of the yeast enzyme, is found within the active site and is loosely conserved amongst several sources of transketolase. To investigate the role of cysteine 160 found in the active site of R. sphaeroides CbbT, this residue was targeted for mutagenesis. Cys160 was changed to alanine, serine, aspartate, and glutamate. To compare the effect of these mutations on ThDP binding, spectral techniques were employed in addition to analysis by enzymatic activity. Fluorescence quenching was used to measure both equilibrium binding constants as well as first order rates of binding. The results of these studies indicated that Cys160 played an important and substantial role in cofactor binding, revealing the importance of this loosely conserved residue. In addition, the Cys160 mutants did not appear to alter oxygen-mediated inactivation.

Thiamin auxotrophy in yeast through altered cofactor dependence of the enzyme acetohydroxyacid synthase

The THI1 gene of Saccharomyces cerevisiae has been identified and found to be allelic with the previously characterized gene ILV2 that encodes acetohydroxyacid synthase (AHAS). This enzyme catalyses the first step in the parallel biosyntheses of the branched-chain amino acids isoleucine and valine, using thiamin pyrophosphate (TPP) as a cofactor. The ilv2-thi1 allele encodes a functional AHAS enzyme with an altered dependence for the cofactor TPP resulting in the thiamin auxotrophic phenotype. Nucleotide sequence analysis and site-directed mutagenesis revealed that the thi1 mutation is a single base substitution which causes the conserved amino acid substitution D176E in the AHAS protein. This study therefore implicates aspartate 176 as another amino acid residue important either for the efficient binding of TPP by AHAS or for the functional stability of the holoenzyme.

Optimum nutrition: thiamin, biotin and pantothenate

The metabolism of glucose is deranged in thiamin deficiency, but once any deficiency has been corrected there is no further effect of increased thiamin intake on the ability to metabolize glucose through either pyruvate dehydrogenase (EC 1.2.4.1) and the citric acid cycle, or the pentose phosphate pathway, in which transketolase (EC 2.2.1.1) is the thiamin-dependent step. It has been suggested that the Wernicke-Korsakoff syndrome is associated with a genetic variant of transketolase which requires a higher than normal concentration of thiamin diphosphate for activity. This finding would suggest that there may be a group of the population who have a higher than average requirement for thiamin, but the evidence is not convincing. There are no estimates of biotin requirements, but either coenzyme saturation of erythrocyte pyruvate carboxylase, or the excretion of 3-hydroxy-isovalerate (perhaps after a test dose of leucine) could be used to assess requirements in depletion-repletion studies. Biotin deficiency leads to impaired glucose tolerance, but it is unlikely that glucose tolerance could be used to assess optimum biotin status, since other more common factors affect glucose tolerance to a greater extent. Plasma triacylglycerol and nonesterified fatty acids are moderately elevated in pantothenic acid deficiency. However, this is unlikely to be useful in assessing pantothenate status, since again, other more common factors affect plasma lipids. To date there are no biochemical indices of adequate pantothenate nutrition, and no estimates of requirements.

Aspartate 155 of human transketolase is essential for thiamine diphosphate-magnesium binding, and cofactor binding is required for dimer formation

Active human transketolase is a homodimeric enzyme possessing two active sites, each with a non-covalently bound thiamine diphosphate and magnesium. Both subunits contribute residues at each site which are involved in cofactor binding and in catalysis. His-tagged transketolase, produced in E. coli, was similar to transketolase purified from human tissues with respect to Km apps for cofactor and substrates and with respect to cofactor-dependent hysteresis. Mutation of aspartate 155, corresponding to a conserved aspartate residue among thiamine diphosphate-binding proteins, resulted in an inactive protein which could not bind the cofactor-magnesium complex and which could not dimerize. The results are consistent with the suggestion that aspartate 155 is an important coordination site for magnesium. In support of this interpretation, binding of cofactor by wild type apo-transketolase required the presence of magnesium. Additionally, monomeric apo-his-transketolase required both magnesium and cofactor binding for dimer formation.