Chaperone mediated solubilization of 69-kDa recombinant maltodextrin glucosidase in Escherichia coli

AIMS

To investigate the factors affecting expression and solubilization of Escherichia coli maltodextrin glucosidase in E. coli.

METHODS AND RESULTS

Expression level and solubilization of the recombinant E. coli maltodextrin glucosidase was studied in E. coli at different temperatures, in presence of overexpressed GroEL, GroES and externally supplemented glycerol. Aggregation of maltodextrin glucosidase in the cytoplasm was partially prevented by the co-expression of GroEL and GroES, and using externally supplemented glycerol or lowering the culture temperature. Co-expression of GroEL and GroES or simultaneous presence of overexpressed GroEL, GroES and externally supplemented glycerol together resulted significant increase of the activity of maltodextrin glucosidase. The growth rate of E. coli was inhibited by the formation of inclusion bodies whereas the presence of overexpressed GroEL, GroES alone or together with glycerol enhanced the growth rate of E. coli substantially.

CONCLUSIONS

The results indicated that lowering the temperature, use of GroEL, GroES and glycerol could be few controlling factors for the solubilization of recombinant aggregation-prone maltodextrin glucosidase in E. coli.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our study could help in developing the strategy for enhancing the production of soluble industrial enzymes and finding the therapeutic agents against protein misfolding diseases.

Comment on "Reconstructing the origin of Andaman islanders"

On the basis of mitochondrial DNA sequence analyses, Thangaraj et al. (Brevia, 13 May 2005, p. 996) proposed that Andaman islanders descended from the first humans to migrate out of Africa. We identified mitochondrial DNA from two northeast Indian Rajbanshi individuals that shares three specific mutations with the M31a lineage observed in the Great Andamanese, which suggests that the predecessor of haplogroup M31 originated on the Indian subcontinent.

Response to Comment on "Reconstructing the Origin of Andaman Islanders"

On the basis of mitochondrial DNA sequence analyses, Thangaraj et al. (Brevia, 13 May 2005, p. 996) proposed that Andaman islanders descended from the first humans to migrate out of Africa. We identified mitochondrial DNA from two northeast Indian Rajbanshi individuals that shares three specific mutations with the M31a lineage observed in the Great Andamanese, which suggests that the predecessor of haplogroup M31 originated on the Indian subcontinent.

HLA-A and HLA-B distribution in Toto - a vanishing sub-Himalayan tribe of India

The frequency of HLA-A and HLA-B locus alleles was studied by using polymerase chain reaction-based sequence-specific primer method in a very primitive and vanishing sub-Himalayan Indian Tribe, the Toto population of North Bengal. The Toto, a Mongoloid tribe with a population size of 1172 reside only in the Totopara of Jalpaiguri district of North Bengal. We studied 40 individuals and observed some high frequency alleles when compared to other Indian tribal, non-tribal, and major world populations. Particularly, the frequency of HLA-B14 was 32.5% in the Toto population, the highest known frequency reported in any population in the world. This indigenous tribal population may harbour novel HLA alleles and unique haplotypes which extensive HLA genotyping will help to reveal, and thus further our understanding of their genetic admixture and migration patterns.

The dazzling array of basal branches in the mtDNA macrohaplogroup M from India as inferred from complete genomes

Many efforts based on complete mitochondrial DNA (mtDNA) genomes have been made to depict the global mtDNA landscape, but the phylogeny of Indian macrohaplogroup M has not yet been resolved in detail. To fill this lacuna, we took the same strategy as in our recent analysis of Indian mtDNA macrohaplogroup N and selected 56 mtDNAs from over 1,200 samples across India for complete sequencing, with the intention to cover all Indian autochthonous M lineages. As a result, the phylogenetic status of previously identified haplogroups based on control-region and/or partial coding-region information, such as M2, M3, M4, M5, M6, M30, and M33, was solidified or redefined here. Moreover, seven novel basal M haplogroups (viz., M34-M40) were identified, and yet another five singular branches of the M phylogeny were discovered in the present study. The comparison of matrilineal components among India, East Asia, Southeast Asia, and Oceania at the deepest level yielded a star-like and nonoverlapping pattern, reflecting a rapid mode of modern human dispersal along the Asian coast after the initial "out-of-Africa" event.

The role of HLA-G in cytokine homeostasis during early pregnancy complicated with maternal infections: a novel etiopathological approach to the neurodevelopmental understanding of schizophrenia

Schizophrenia is perhaps the most enigmatic and tragic psychotic disorder with remarkable mortality and morbidity. Schizophrenia is complex and clinically a heterogeneous disorder. The etiological basis of schizophrenia ranges from autoimmune to neurodevelopmental hypothesis in one hand and involvement of different major gene segment with susceptibility loci on the other. Recently, neurodevelopmental hypothesis gained much impetus over the other domain. To support the neurodevelopmental basis, a number of investigations have shown that maternal infections during pregnancy increases the risk of the offspring developing schizophrenia and other neurodevelopmental disorders. The pathological mechanisms underlying this phenomenon is largely unknown. Many have suggested the involvement of different immune markers and shown that cytokines generated in response to maternal infection alter early brain development through their inflammatory activity. However, these findings have escaped discussion on various important issues related to cytokine homeostasis which depends on a large number of immune parameters including non-classical HLA-G molecules. Infections during early stages of pregnancy may alter cytokine regulation by disturbing the whole uterine immune milieu. To elucidate this issue, authors have tried to correlate the possible relationships between maternal infections and aberration of immune networking at the feto-maternal interface and their subsequent influence on the structural and functional abnormalities of the developing brain. The authors hypothesize that there exists a counter regulatory interaction among proinflammatory cytokines like TNF-alpha, HLA-G molecules and different immune cells like NK cells. We emphasize that HLA-G molecules are the novel immune players which maintain the immune homeostasis during early pregnancy in a manner that it can protect developing fetus from maternal immune attack. However, maternal infections may lead to the disturbance of HLA-G expression which in turn may fail to maintain its otherwise inhibitory potential to down regulate the detrimental inflammatory cytokines. Investigation on such interaction may unravel novel molecular mechanisms of neurodevelopmental basis of schizophrenia. Testing of our proposed hypothesis on animal models and on in vitro derived extravillous trophoblast cell lines holds promise of great insights to usher a new dimension of schizophrenia research and for developing new therapeutic strategies for better treatment and to adopt genetic prediction in schizophrenia management paradigm.

Phylogeny of mitochondrial DNA macrohaplogroup N in India, based on complete sequencing: implications for the peopling of South Asia

To resolve the phylogeny of the autochthonous mitochondrial DNA (mtDNA) haplogroups of India and determine the relationship between the Indian and western Eurasian mtDNA pools more precisely, a diverse subset of 75 macrohaplogroup N lineages was chosen for complete sequencing from a collection of >800 control-region sequences sampled across India. We identified five new autochthonous haplogroups (R7, R8, R30, R31, and N5) and fully characterized the autochthonous haplogroups (R5, R6, N1d, U2a, U2b, and U2c) that were previously described only by first hypervariable segment (HVS-I) sequencing and coding-region restriction-fragment-length polymorphism analysis. Our findings demonstrate that the Indian mtDNA pool, even when restricted to macrohaplogroup N, harbors at least as many deepest-branching lineages as the western Eurasian mtDNA pool. Moreover, the distribution of the earliest branches within haplogroups M, N, and R across Eurasia and Oceania provides additional evidence for a three-founder-mtDNA scenario and a single migration route out of Africa.

GroEL/GroES-mediated folding of a protein too large to be encapsulated

The chaperonin GroEL binds nonnative proteins too large to fit inside the productive GroEL-GroES cis cavity, but whether and how it assists their folding has remained unanswered. We have examined yeast mitochondrial aconitase, an 82 kDa monomeric Fe(4)S(4) cluster-containing enzyme, observed to aggregate in chaperonin-deficient mitochondria. We observed that aconitase folding both in vivo and in vitro requires both GroEL and GroES, and proceeds via multiple rounds of binding and release. Unlike the folding of smaller substrates, however, this mechanism does not involve cis encapsulation but, rather, requires GroES binding to the trans ring to release nonnative substrate, which likely folds in solution. Following the phase of ATP/GroES-dependent refolding, GroEL stably bound apoaconitase, releasing active holoenzyme upon Fe(4)S(4) cofactor formation, independent of ATP and GroES.

Equilibrium and kinetic studies on folding of the authentic and recombinant forms of human alpha-lactalbumin by circular dichroism spectroscopy

The equilibrium and kinetics of the unfolding and refolding of authentic and recombinant human alpha-lactalbumin, the latter of which had an extra methionine residue at the N-terminus, were studied by circular dichroism spectroscopy, and the results were compared with the results for bovine and goat alpha-lactalbumins obtained in our previous studies. As observed in the bovine and goat proteins, the presence of the extra methionine residue in the recombinant protein remarkably destabilized the native state, and the destabilization was entirely ascribed to an increase in the rate of unfolding. The thermodynamic stability of the native state against the unfolded state was lower, and the thermodynamic stability of the molten globule state against the unfolded state was higher for the human protein than for the other alpha-lactalbumins previously studied. Thus, the population of the molten globule intermediate was higher during the equilibrium unfolding of human alpha-lactalbumin by guanidine hydrochloride. Unlike the molten globule states of the bovine and goat proteins, the human alpha-lactalbumin molten globule showed remarkably more intense circular dichroism ellipticity than the native state in the far-ultraviolet region below 225 nm. During refolding from the unfolded state, human alpha-lactalbumin thus exhibited overshoot kinetics, in which the alpha-helical peptide ellipticity exceeded the native value when the molten globule folding intermediate was formed in the burst phase. The subsequent folding involved reorganization of nonnative secondary structures. It should be noted that the rate constant of the major refolding phase was approximately the same among the three types of alpha-lactalbumin and that the rate constant of unfolding was accelerated 18-600 times in the human protein, and these results interpreted the lower thermodynamic stability of this protein.

Role of hla class-I antigens in delusional disorder

The investigation was conducted to find out whether there is any association between delusional disorder and HLA antigens. The sample comprised 50 patients with delusional disorder and 282 control samples collected from normal controls. Statistical analysis revealed that the frequency of A3 antigen of the locus A are significantly higher. In case of HLA - B locus significantly higher frequency of B5 and B21 antigens have also been observed. The present study shows that there may be some association of HLA class-1 antigens with delusional disorder.

Acute mesenteric ischemia and malpractice claims

BACKGROUND

Acute mesenteric ischemia can be a difficult diagnosis to make, but delay contributes directly to infarction, and this may provide a setting for malpractice claims.

METHODS

We reviewed 180 consecutive malpractice claims submitted by attorneys for medical expert (ME) review during the 12 years ending in late 1998. Seven cases involved acute mesenteric ischemia.

RESULTS

Alleged failure to make a timely diagnosis was the basis for 5 of these claims, failure to provide anticoagulant protection for 1, and failure to prevent nonocclusive ischemic infarction for 1. Six claims were closed after ME review and 1 claim involving late diagnosis was settled before trial.

CONCLUSIONS

The risk of a malpractice claim is reduced by consideration of computed tomography (CT), angiography, and surgical consultation as soon as a patient is seen whose differential diagnosis includes acute mesenteric ischemia.

Necrotizing fasciitis and malpractice claims

BACKGROUND

Necrotizing fasciitis (NF) is an aggressive bacterial infection of the superficial fascia and subcutaneous tissues that is increasing in incidence. The high toll exacted by this illness provides a setting for malpractice claims.

METHOD

We reviewed 180 consecutive malpractice claims submitted by attorneys for medical expert review between 1987 and late 1997. Four cases involved NF.

RESULTS

Alleged failure to obtain timely surgical consultation was the basis for three claims, and alleged failure to prevent NF by proper nursing care was the basis for the fourth. Three cases were closed and one was settled.

CONCLUSIONS

The cornerstone of risk management for a clinical presentation compatible with NF is immediate surgical consultation, with other diagnostic steps a secondary consideration.

Effect of the extra n-terminal methionine residue on the stability and folding of recombinant alpha-lactalbumin expressed in Escherichia coli

The structure, stability, and unfolding-refolding kinetics of Escherichia coli-expressed recombinant goat alpha-lactalbumin were studied by circular dichroism spectroscopy, X-ray crystallography, and stopped-flow measurements, and the results were compared with those of the authentic protein prepared from goat milk. The electric properties of the two proteins were also studied by gel electrophoresis and ion-exchange chromatography. Although the overall structures of the authentic and recombinant proteins are the same, the extra methionine residue at the N terminus of the recombinant protein remarkably affects the native-state stability and the electric properties. The native state of the recombinant protein was 3.5 kcal/mol less stable than the authentic protein, and the recombinant protein was more negatively charged than the authentic one. The recombinant protein unfolded 5.7 times faster than the authentic one, although there were no significant differences in the refolding rates of the two proteins. The destabilization of the recombinant protein can be fully interpreted in terms of the increased unfolding rate of the protein, indicating that the N-terminal region remains unorganized in the transition state of refolding, and hence is not involved in the folding initiation site of the protein. A comparison of the X-ray structures of recombinant alpha-lactalbumin determined here with that of the authentic protein shows that the structural differences between the proteins are confined to the N-terminal region. Theoretical considerations for the differences in the conformational and solvation free energies between the proteins show that the destabilization of the recombinant protein is primarily due to excess conformational entropy of the N-terminal methionine residue in the unfolded state, and also due to less exposure of hydrophobic surface on unfolding. The results suggest that when the N-terminal region of a protein has a rigid structure, expression of the protein by E. coli, which adds the extra methionine residue, destabilizes the native state through a conformational entropy effect. It also shows that differences in the electrostatic interactions of the N-terminal amino group with the side-chain atoms of Thr38, Asp37, and Asp83 bring about a difference in the pKa value of the N-terminal amino group between the proteins, resulting in a greater negative net charge of the recombinant protein at neutral pH.

Pulmonary embolism and malpractice claims

BACKGROUND

Deep venous thrombosis (DVT) with pulmonary embolization (PE) often occurs as an unexpected event with fatal consequences. This provides a setting for malpractice claims.

METHODS

We reviewed 160 consecutive malpractice claims submitted by attorneys for medical expert review during the 11-year period ending in 1997. Seven cases involved DVT with PE.

RESULTS

Alleged failure to anticipate and reduce the chance of PE was the basis for six of the claims. All six patients were at risk for lower extremity DVT, and one had a history of DVT 6 months earlier. The PE was manifested by sudden death in three cases. The seventh case represented a complication of heparin therapy for PE.

CONCLUSIONS

We conclude that risk management for PE should focus primarily on DVT. Physicians should perform and document an examination for DVT whenever there is a history of lower extremity stasis or it is likely to occur. They should also consider documenting a concurring second opinion when making anticoagulant-related decisions.

Role of radionuclide phallogram in therapeutic decision-making for erectile dysfunction

OBJECTIVE

The purpose of this study is to evaluate the role of radionuclide phallograms in therapeutic decision-making for erectile dysfunction.

METHOD

Forty-eight impotent men being considered for pharmacologically-induced penile erection therapy (PIPE) had radionuclide phallograms (RP) as part of their evaluation. RP were performed using 99mTc-labeled autologous red blood cells and provided a measurement of penile blood volume (PBV) change following the intracorporeal injection of 0.25 to 0.3 mL of a papaverine/phentolamine mixture.

RESULTS

Thirty-eight patients showed a good response with a mean PBV increase 2.6 times baseline (range 1.2 to 8.9). Ten patients had significantly lower PBV changes (P = 0.001) than the first group, with a mean PBV increase of 1.6 times baseline (range 1.1 to 2.4). These ten patients were dissatisfied with pharmacologically induced penile erection (PIPE) therapy after an unsuccessful treatment trial.

CONCLUSION

We conclude that the RP can help to discriminate between patients who will benefit from PIPE therapy and those who will not.

Stroke and malpractice claims

We describe 15 malpractice claims that were filed after the patients had strokes. Both embolic and thrombotic, sterile and infected strokes led to claims. Ten of the claims alleged physician failure to protect the patient, two alleged physician failure to react as called for by symptoms, and three were related to medication. We conclude that physicians should advise patients of the possibility of stroke when circumstances warrant it, as well as documenting their judgment and suggested preventive practices. These cases further suggest that treatment decisions supported by documented second opinions may reduce the number of malpractice claims for strokes.

Refolding kinetics of partially reduced and S-carboxymethylated trypsin-subtilisin inhibitor from marine turtle eggwhite

Three accessible disulphide bonds of basic trypsin-subtilisin inhibitor from marine turtle eggwhite have been reduced with 0.1M NaBH4 at 0 degree C under nitrogen atmosphere at pH9.8 and then S-carboxymethylated. The partially reduced inhibitor retains 80% of the native inhibitory activity towards trypsin and subtilisin. The S-carboxymethylated inhibitor undergoes slower refolding than the native inhibitor from its fully denatured and reduced state at pH 8.5 in the presence of oxidised and reduced glutathione. The refolding process was characterised by the attainment of the inhibitory activity towards trypsin and subtilisin. The values of the second order rate constant for the refolding reactions of the modified protein are 0.02 x 10(2)M-1sec1 and 0.033 x 10(2)M-1sec-1 for its trypsin and subtilisin inhibiting domains and their energies of activation are 20.1 Kcal/mole and 24.6 Kcal/mole. The partially modified inhibitor does not regain complete inhibitory activity even after long incubation in the oxido-shuffling buffer. From the above findings it can be concluded that the three disulphide bonds of the native inhibitor are not essential for the inhibitory activity of the trypsin-subtilisin inhibitor but they help in the correct refolding of the inhibitor by forming transient disulphide bonds with the external disulphide reagents as well as with the internal sulphydryl groups.

Iatrogenic hypoglycemia and malpractice claims

Iatrogenic neuroglycopenia represents a medical emergency for which accepted and usually effective treatment exists. Treating physicians face a malpractice risk if there is permanent neurologic damage and there is a perception of failure to act prudently both before and after the damaging episode. We report two cases to illustrate the medical and legal issues that may be raised in such claims.

Refolding of trypsin-subtilisin inhibitor from marine turtle eggwhite

Trypsin-subtilisin inhibitor from marine turtle eggwhite refolded quantitatively from its fully reduced state at pH 8.5 in the presence of reduced and oxidized glutathione. The refolding process was studied by following the accompanying changes in inhibitory activity, fluorescence, sulfhydryl group titer, and hydrodynamic volume. The refolding process followed second-order kinetics with rate constants of 4.80 x 10(2) M-1 sec-1 for trypsin-inhibiting domain and 0.77 x 10(2) M-1 sec-1 for subtilisin-inhibiting domain of the inhibitor at 30 degrees C and their respective activation energies of the refolding process were 15.9 and 21.6 kcal/mol. Fluorescence intensity of the reduced inhibitor decreased with time of refolding until it corresponded to the intensity of the native inhibitor. The inhibitor contained 1-2% alpha-helix, 40-42% beta-sheet, and 57-58% random coil structure. Refolded inhibitor gave a circular dichroic spectrum identical to that of the native inhibitor. A number of principal intermediates were detected as a function of the refolding time. Size-exclusion chromatography separated the intermediates differing in hydrodynamic volume (Stokes radius). The Stokes radius ranged from 23 A (fully reduced inhibitor) to 18.8 A (native inhibitor). Results indicated the independent refolding of two domains of the inhibitor and multiple pathways of folding were followed rather than an ordered sequential pathway.