Identification of Chlamydia trachomatis CT621, a protein delivered through the type III secretion system to the host cell cytoplasm and nucleus

Chlamydiae are obligate intracellular bacteria, developing inside host cells within chlamydial inclusions. From these inclusions, the chlamydiae secrete proteins into the host cell cytoplasm. A pathway through which secreted proteins can be delivered is the type III secretion system (T3SS). The T3SS is common to several gram-negative bacteria and the secreted proteins serve a variety of functions often related to the modulation of host signalling. To identify new potentially secreted proteins, the cytoplasm was extracted from Chlamydia trachomatis L2-infected HeLa cells, and two-dimensional polyacrylamide gel electrophoresis profiles of [³⁵S]-labelled chlamydial proteins from this extract were compared with profiles of chlamydial proteins from the lysate of infected cells. In this way, CT621 was identified. CT621 is a member of a family of proteins containing a domain of unknown function DUF582 that is only found within the genus Chlamydia . Immunofluorescence microscopy and immunoblotting demonstrated that CT621 is secreted late in the chlamydial developmental cycle and that it is the first chlamydial protein found to be localized within both the host cell cytoplasm and the nucleus. To determine whether CT621 is secreted through the T3SS, an inhibitor of this apparatus was added to the infection medium, resulting in retention of the protein inside the chlamydiae. Hence, the so far uncharacterized CT621 is a new type III secretion effector protein.     

Synthesis,structure–activity relationship and crystallographic studies of 3-substituted indolin-2-one RET inhibitors

The synthesis, structure–activity relationships (SAR) and structural data of a series of indolin-2-one inhibitors of RET tyrosine kinase are described. These compounds were designed to explore the available space around the indolinone scaffold within RET active site. Several substitutions at different positions were tested and biochemical data were used to draw a molecular model of steric and electrostatic interactions, which can be applied to design more potent and selective RET inhibitors. The crystal structures of RET kinase domain in complex with three inhibitors were solved. All three compounds bound in the ATP pocket and formed two hydrogen bonds with the kinase hinge region. Crystallographic analysis confirmed predictions from molecular modelling and helped refine SAR results. These data provide important information for the development of indolinone inhibitors for the treatment of RET-driven cancers.     

Rapid and efficient FBN1 mutation detection using automated sample preparation and direct sequencing as the primary strategy

Mutations in the fibrillin-1 (FBN1) gene cause Marfan syndrome (MFS) and the other type-1 fibrillinopathies. Finding these mutations is a major challenge considering that the FBN1 gene has a coding region of 8,600 base pairs divided into 65 exons. Most of the more than 600 known mutations have been identified using a mutation scanning method prior to sequencing of fragments with a suspected mutation. However, it is not obvious that these screening methods are ideal, considering cost, efficiency, and sensitivity. We have sequenced the entire FBN1 coding sequence and flanking intronic sequences in samples from 105 patients with suspected MFS, taking advantage of robotic devices, which reduce the cost of supplies and the quantity of manual work. In addition, automation avoids many tedious steps, thus reducing the opportunity for human error. Automated assembling of PCR, purification of PCR products, and assembly of sequencing reactions resulted in completion of the FBN1 sequence in half of the time needed for the manual protocol. Mutations were identified in 69 individuals. The mutation detection rate (76%), types, and genetic distribution of mutations resemble the findings in other MFS populations. We conclude that automated sequencing using the robotic systems is well suited as a primary strategy for diagnostic mutation identification in FBN1.     

Increased central facilitation of antagonist reciprocal inhibition at the onset of dorsiflexion following explosive strength training

At the onset of dorsiflexion disynaptic reciprocal inhibition (DRI) of soleus motoneurons is increased to prevent activation of the antagonistic plantar flexors. This is caused by descending facilitation of transmission in the DRI pathway. Because the risk of eliciting stretch reflexes in the ankle plantar flexors at the onset of dorsiflexion is larger the quicker the movement, it was hypothesized that DRI may be increased when subjects are trained to perform dorsiflexion movements as quickly as possible For this purpose, 14 healthy human subjects participated in explosive strength training of the ankle dorsiflexor muscles 3 times a week for 4 wk. Test sessions were conducted before, shortly after, and 2 wk after the training period. The rate of torque development measured at 30, 50, 100, and 200 ms after onset of voluntary explosive isometric dorsiflexion increased by 24-33% (P < 0.05). DRI was measured as the depression of the soleus H reflex following conditioning stimulation of the peroneal nerve (1.1 x motor threshold) at an interval of 2-3 ms. At the onset of dorsiflexion the amount of DRI measured relative to DRI at rest increased significantly from 6% before the training to 22% after the training (P < 0.05). We speculate that DRI at the onset of movement may be increased in healthy subjects following explosive strength training to ensure efficient suppression of the antagonist muscles as the dorsiflexion movement becomes faster.     

Crystallographic and solution studies of N-lithocholyl insulin: a new generation of prolonged-acting human insulins

The addition of specific bulky hydrophobic groups to the insulin molecule provides it with affinity for circulating serum albumin and enables it to form soluble macromolecular complexes at the site of subcutaneous injection, thereby securing slow absorption of the insulin analogue into the blood stream and prolonging its half-life once there. N-Lithocholic acid acylated insulin [Lys(B29)-lithocholyl des-(B30) human insulin] has been crystallized and the structure determined by X-ray crystallography at 1.6 A resolution to explore the molecular basis of its assembly. The unit cell in the crystal consists of an insulin hexamer containing two zinc ions, with two m-cresol molecules bound at each dimer-dimer interface stabilizing an R(6) conformation. Six covalently bound lithocholyl groups are arranged symmetrically around the outside of the hexamer. These form specific van der Waals and hydrogen-bonding interactions at the interfaces between neighboring hexamers, possibly representing the kinds of interactions which occur in the soluble aggregates at the site of injection. Comparison with an equivalent nonderivatized native insulin hexamer shows that the addition of the lithocholyl group disrupts neither the important conformational features of the insulin molecule nor its hexamer-forming ability. Indeed, binding studies show that the affinity of N-lithocholyl insulin for the human insulin receptor is not significantly diminished.     

In vitro deamination of cytosine to uracil in single-stranded DNA by apolipoprotein B editing complex catalytic subunit 1 (APOBEC1)

Apolipoprotein B-editing complex catalytic subunit 1 (APOBEC1) is the catalytic component of an RNA-editing complex that deaminates C6666 --> U in apolipoprotein B RNA in gastrointestinal tissue, thereby generating a premature stop codon. Whereas RNA is the physiological substrate of APOBEC1, recent experiments have strongly indicated that, when expressed in bacteria, APOBEC1 and some of its homologues can deaminate cytosine in DNA. Indeed, genetic evidence demonstrates that the physiological function of activation-induced deaminase, a B lymphocyte-specific APOBEC1 homologue, is to perform targeted deamination of cytosine within the immunoglobulin locus, thereby triggering antibody gene diversification. However, biochemical evidence of in vitro DNA deamination by members of the APOBEC family is still needed. Here, we show that deamination of cytosine to uracil in DNA can be achieved in vitro using partially purified APOBEC1 from extracts of transformed Escherichia coli. Thus, APOBEC1 can deaminate cytosine in both RNA and DNA. Strikingly, its activity on DNA is specific for single-stranded DNA and exhibits dependence on local sequence context.     

Mutational analysis of the human FATE gene in 144 infertile men

The FATE gene maps to Xq28 where one case of a translocation breakpoint has been found in an infertile man. Moreover, the FATE promoter contains a putative SF-1-binding site, and FATE has been proposed as representing a target gene of SF-1 in testicular development or germ cell differentiation. This study presents a complete mutational screening of the FATE gene in a random group of 144 infertile males. Four polymorphisms and two mutations were found. Three of the polymorphisms, viz., 741CT, 905AC, and 3985CT, occurred in exon 5 and intron 2 and did not alter the deduced polypeptide. One polymorphism resulted in the conservative amino acid exchange, A10 V, in 16.0% of the patients. This substitution occurred with similar frequencies in the control groups, indicating that the mutation does not affect fertility in men or women. The two mutations caused the non-conservative amino acid substitutions S125R (patient 1) and I34T (patient 2). A family study (patient 1) revealed, however, that S125R was inherited and that a fertile male family member carried the mutation. Patient 2 did not have relevant family members who could be examined. Thus, this study has shown that only 1.4% of infertile men have mutations in the FATE gene, and that some of these mutations do not singly cause infertility. Hence, FATE may not play an important role in the disease-state of infertile men attending fertility clinics. However, FATE mutations cannot be excluded as being a contributing factor in some cases of male infertility.     

Mercury decreases culturability of Pseudomonas frederiksbergensis JAJ 28 in soil microcosms

Mercury is a biologically potent heavy metal, which has been found to change the diversity of culturable bacteria. Therefore, we investigated whether Hg kills bacteria in soil or reduces culturability. Soil microcosms were inoculated with Pseudomonas frederiksbergensis JAJ 28 and were sampled regularly during 28 days. The total number of acridine orange-stained cells was relatively constant, and Hg reduced the number on only one sampling day. However, the fraction of culturable cells on 1/10 tryptic soy agar was lowered on days 6, 13, and 21. The number of microcolony forming units, which represents viable cells, was also affected by Hg, but this effect was delayed compared with the effects on CFUs. The amount of headspace CO2 per cell was overall increased by Hg, another indication of the toxic effects of Hg on the bacterial cells. Our results thus emphasize the need to take culturability into account when studying the effects of heavy metals on bacterial diversity.     

Thalidomide inhibits early atherogenesis in apoE-deficient mice

Inflammation is present in all stages of atherosclerosis, from fatty streaks to rupture of mature plaques. Tumour necrosis factor (TNF)-alpha is expressed in atherosclerotic lesions but its role in atherogenesis has not been defined. To clarify the role of this cytokine, we administered thalidomide, a compound known to inhibit TNF-alpha production, to homozygous apolipoprotein E-deficient (apoE-/-) mice in order to examine the effect of thalidomide on the development of early atherosclerotic lesions. Twelve apoE-/- mice were randomized to receive either sustained-release thalidomide or placebo pellets implanted subcutaneously, and the amount of atherosclerosis was quantified six weeks later. Thalidomide was well tolerated and did not result in any changes in body weight. Mice treated with thalidomide had significantly smaller mean (7986 +/- 5189 vs 19607 +/- 10353 microns 2, p = 0.05) and maximum (15800 [12777-23675] vs 37169 [28000-41351] microns 2, p = 0.03) lesion sizes than those treated with placebo. Thus, thalidomide is capable of inhibiting the early development of atherosclerosis, presumably by inhibition of TNF-alpha secretion.     

Engineering-enhanced protein secretory expression in yeast with application to insulin

Adaptation to efficient heterologous expression is a prerequisite for recombinant proteins to fulfill their clinical and biotechnological potential. We describe a rational strategy to optimize the secretion efficiency in yeast of an insulin precursor by structure-based engineering of the folding stability. The yield of a fast-acting insulin analogue (Asp(B28)) expressed in yeast was enhanced 5-fold by engineering a specific interaction between an aromatic amino acid in the connecting peptide and a phenol binding site in the hydrophobic core of the molecule. This insulin precursor is characterized by significantly enhanced folding stability. The improved folding properties enhanced the secretion efficiency of the insulin precursor from 10 to 50%. The precursor remains fully in vitro convertible to mature fast-acting insulin.