Retrospective Analysis of Vision Rehabilitation for Veterans With Traumatic Brain Injury-Related Vision Dysfunction

INTRODUCTION

Traumatic brain injury (TBI) can trigger vision-based sequelae such as oculomotor and accommodative abnormalities, visual-vestibular integrative dysfunction, visual field loss, and photosensitivity. The need for diagnosis and management of TBI-related vision impairment has increased because of the increasing frequencies of combat warfighters returning from Iraq and Afghanistan with TBIs. The purpose of this research was to learn the sequelae of rehabilitation service delivery to veterans with TBI-related visual dysfunction after they are diagnosed. To accomplish this, we investigated vision rehabilitation assessments and interventions provided to veterans with TBI-related visual dysfunction at the Department of Veterans Affairs (VA) specialty polytrauma facilities for the 2 years following their injury. The research questions asked what assessments, interventions, and prescribed assistive devices were provided by VA specialty clinics (e.g., occupational therapy, polytrauma, and blind rehabilitation) and how service delivery was affected by demographic and clinical variables.

MATERIALS AND METHODS

A retrospective design was used to analyze VA data using natural language processing of unstructured clinician notes and logistic regression of structured data. Participants included 350 veterans with TBI who received rehabilitation at one of the five VA Polytrauma Rehabilitation Centers (Tampa, FL; Richmond, VA; Minneapolis, MN; San Antonio, TX; and Palo Alto, CA) between 2008 and 2017 and who were administered the 2008 congressionally mandated "Traumatic Brain Injury Specific Ocular Health and Visual Functioning Exam." The outcome variables were vision assessments, interventions, and prescribed assistive technology discovered via natural language processing of clinician notes as well as the vision rehabilitation specialty clinics providing the clinical care (polytrauma, occupational therapy, outpatient blind rehabilitation, inpatient blind rehabilitation, optometry, and low vision) extracted from VA structured administrative data.

RESULTS

Veterans receiving rehabilitation for TBI-related vision dysfunction were most frequently assessed for saccades, accommodation, visual field, and convergence. Intervention was provided most frequently for eye-hand coordination, saccades, accommodation, vergence, and binocular dysfunction. Technology provided included eyeglasses, wheelchair/scooter, walker/cane, aids for the blind, and computer. There was an overlap in the services provided by specialty clinics. Services available and delivered were significantly associated with the comorbidities of each patient and the specialty clinics available at each VA Polytrauma Rehabilitation Center.

CONCLUSIONS

The delivery of patient services should be driven by the needs of veterans and not by system-level factors such as the availability of specific vision rehabilitation services at specific locations. Traditional low vision and blind rehabilitation programs were not designed to treat the comorbidities and symptoms associated with TBI. To address this challenge, blind rehabilitation and neurologic recovery cross training is needed. Our findings document how five VA Polytrauma Rehabilitation Centers implemented this training in 2008. The next step is to extend and standardize this new paradigm to community care, where these post-deployment patients now reside.

Veterans with Traumatic Brain Injury-related Ocular Injury and Vision Dysfunction: Vision Rehabilitation Utilization

SIGNIFICANCE

Visual dysfunction is frequently associated with traumatic brain injury (TBI). Although evidence regarding the prevalence of symptoms of this population has been published, little is known about health care utilization. A retrospective review of the data derived from the Department of Veterans Affairs (VA)-mandated "Traumatic Brain Injury Specific Ocular Health and Visual Functioning Examination for Polytrauma Rehabilitation Center Patients" provided a unique opportunity to investigate vision rehabilitation utilization.

PURPOSE

The purpose of this study was to understand (a) the frequency of vision rehabilitation follow-up visits at 6, 12, and 24 months; (b) the association between follow-up and demographic, comorbidity, and severity of TBI covariates as well as ocular and visual symptoms, geographic access, and evaluating facility; and (c) why some veterans did not follow up with recommendations.

METHODS

Retrospective and survey designs were used. The sample included 2458 veterans who served in the Operation Enduring Freedom/Operation Iraqi Freedom conflicts and received care at one of the five VA Polytrauma Rehabilitation Centers between January 1, 2008, and December 31, 2017. Quantitative and qualitative descriptive analyses and stepwise logistic regression were performed.

RESULTS

About 60% of veterans followed up with recommended vision rehabilitation with visits equally split between VA Polytrauma Rehabilitation Centers and community VA facilities. For each 10-year increase in age, there was a corresponding reduction of 12% in the odds of follow-up. Veterans with decreased visual field had 50% greater odds of follow-up than those who did not. Veterans with difficulty reading had 59% greater odds of follow-up than those who did not. Those who had a double vision had 45% greater odds of follow-up than those who did not.

CONCLUSIONS

Our findings suggest that the need for vision rehabilitation may extend as long as 2 years after TBI. Access to vision rehabilitation is complicated by the paucity of available neuro-optometric services.

Veterans with Traumatic Brain Injury-related Ocular Injury and Vision Dysfunction: Recommendations for Rehabilitation

SIGNIFICANCE

We know the prevalence of traumatic brain injury (TBI)-related vision impairment and ocular injury symptoms. Lacking is an understanding of health care utilization to treat these symptoms. Utilization knowledge is important to structuring access to treatment, identifying clinical training needs, and providing evidence of the effectiveness of treatment.

PURPOSE

This article reports rehabilitation, glasses/contacts, and imaging/photography/video recommendations made by optometrists and ophthalmologists as part of the Department of Veterans Affairs-mandated Performance of Traumatic Brain Injury Specific Ocular Health and Visual Functioning Examination administered to veterans with TBI at Department of Veterans Affairs polytrauma specialty facilities.

METHODS

Using a retrospective design, natural language processing, and descriptive and regression statistics, data were analyzed for 2458 Operation Enduring Freedom/Operation Iraqi Freedom veterans who were administered the mandated examination between 2008 and 2017.

RESULTS

Of the 2458 veterans, vision rehabilitation was recommended for 24%, glasses/contacts were recommended for 57%, and further imaging/photography/video testing was recommended for 58%. Using key words in the referral, we determined that 37% of veterans were referred to blind rehabilitation, 16% to occupational therapy, and 3% to low-vision clinics. More than 50% of the referrals could have been treated by blind rehabilitation, occupational therapy, or low-vision clinics. Rehabilitation referrals were significantly associated with younger age, floaters, photosensitivity, double vision, visual field and balance deficits, dizziness, and difficulty reading. In comparison, prescriptions for glasses and contacts were associated with older age, photosensitivity, blurred vision, decreased visual field and night vision, difficulty reading, and dry eye. Imaging/photography/video testing was associated with floaters, photosensitivity, and headache.

CONCLUSIONS

Findings delineate service delivery models available to veterans with TBI-related vision impairment. The challenge these data address is the lack of clear paths from diagnosis of TBI to identification of vision dysfunction deficits to specialized vision rehabilitation, and finally to community reintegration and community based-vision rehabilitation.

Development and Psychometric Properties of the Self-Blame Attributions for Cancer Scale

OBJECTIVES

To adapt the Cardiac Self-Blame Attributions Scale into the Self-Blame Attributions for Cancer Scale (SBAC) for use in patients with cancer and analyze its psychometric properties.

SAMPLE & SETTING

113 patients receiving radiation therapy at the University of Kansas Cancer Center.

METHODS & VARIABLES

The SBAC and other self-report measures were administered during outpatient oncology appointments for radiation therapy to establish the psychometric properties of the SBAC.

RESULTS

A two-factor structure represented behavioral and characterological self-blame attributions. Reliability estimates for each factor were excellent and evidence of convergent and discriminant validity was found, indicating support for the SBAC as a valid and reliable measure of self-blame attributions in patients with cancer.

IMPLICATIONS FOR NURSING

The SBAC may help healthcare providers, including nursing staff, to identify the self-blame patterns exhibited by patients with cancer. Future research can assess the reliability and validity of SBAC across stages of treatment and establish the predictive validity of the scale in individuals with cancer.

DISENTANGLING KNOWLEDGE AND BIAS: COMBATING AGEISM WITH THE REVISED FACTS ON AGING QUIZ

The Facts on Aging Quiz (FoAQ) was developed in 1977 as a 25-item True/False test of knowledge about older adults. Since that time, it has been utilized in hundreds of studies involving clarifying misconceptions, measuring factual knowledge across different groups, and assessing bias toward older adults. The current study examines the psychometric properties of a revision to the FoAQ created in 2015 that modified the original items and added 25 more to better reflect contemporary aging research. Participants were sampled using Qualtrics and MTurk platforms and targeted to equally represent the following four age groups: 18-34, 35-49, 50-64, and 65 and older. Exploratory factor analysis (n=956) did not support a multi-factor structure, contrary to previous theories of it having cognitive, physical, societal, and psychological health factors. A single factor model was forced which contained 28 items that only accounted for 26% of the variance in scores. The reliability reached satisfactory levels in the younger three age groups with the 28-item version but remained inadequate among those 65 and older. Small associations with the Expectations Regarding Aging-12 and Aging Semantic Differential scales were observed. In its present format, the FoAQ is not sufficient for research use but remains a useful tool in provoking discussion about age bias and areas in which people of all ages lack factual information. Researchers suggest an expansion in response options and further clarifying the use of this instrument as a measure of knowledge or bias.

Abstract P4-03-02: Characterizing and targeting chemoresistant subclones in patient-derived xenograft models of triple negative breast cancer

Fifty percent of all triple negative breast cancer (TNBC) patients harbor significant residual tumor burden following treatment with standard neoadjuvant chemotherapy (NACT), resulting in poor prognosis. Recent studies in TNBC have revealed extensive intra-tumoral heterogeneity at the time of diagnosis and throughout disease progression, but the relative contributions of these heterogeneous populations of tumor cells to chemoresistance are not well understood.

The primary tumor, dermal metastasis, and germline reference were obtained from a patient with untreated metastatic TNBC. Tumor cells were engrafted into the humanized mammary fat pads of NOD/SCID mice to establish PDX models of the primary (PIM001-P) and metastatic (PIM001-M) tumors. RNA sequencing and whole-exome sequencing (WES), performed on the patient's primary and metastatic tumors and the first- and third- passage PDX models revealed transcriptomic profiles and subclonal heterogeneity of the patient's tumors were recapitulated in the PDX models.

Treatment of mice engrafted with PIM001-P tumors with NACT (Adriamycin plus cyclophosphamide, AC) resulted in partial response, the magnitude of which was diminished in mice bearing PIM001-M tumors. Tumor subclones were tracked during chemotherapy treatment in mice engrafted with PIM001-P tumors using lentiviral non-targeting DNA barcodes. Residual tumors maintained the clonal architecture of untreated tumors, and deep WES revealed stable maintenance of somatic mutant allele frequencies throughout treatment. Therefore, selection of pre-existing resistant clones did not lead to AC resistance in this model. Interestingly, only 25% of residual tumor clones contributed to primary relapse once treatment was halted, suggesting only a subpopulation of tumor cells was able to reconstitute the tumor.

RNA sequencing and reverse phase protein array revealed that while vehicle-treated and regrown tumors were highly similar, residual tumors harbored a unique profile characterized by numerous significant alterations in RNA and protein levels. Together, these results suggest that residual tumors enter into a transient drug-resistant state that is reversible. Residual tumors were enriched for alterations in pathways such as metabolism, extracellular matrix remodeling, and cell-cell communication. Pharmacologic targeting of the residual tumor state with an inhibitor of mitochondrial oxidative phosphorylation led to significant inhibition of tumor regrowth following AC treatment. Additional vulnerabilities identified in residual tumors are being targeted therapeutically with the goal of eradicating residual tumor cells.

Citation Format: Echeverria GV, Seth S, Ge Z, Sun Y, DiFrancesco E, Lau R, Marszalek J, Moulder S, Symmans F, Heffernan TP, Chang JT, Piwnica-Worms H. Characterizing and targeting chemoresistant subclones in patient-derived xenograft models of triple negative breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P4-03-02.

Formulation of dacarbazine-loaded Cubosomes--part II: influence of process parameters

The purpose of this study is to investigate the combined influence of process parameters (independent variables) such as homogenization speed (X(1)), duration (X(2)), and temperature (X(3)) during the preparation of dacarbazine-loaded cubosomes. Box-Behnken design was used to rationalize the influence of these three factors on two responses, namely particle size (Y(1)) and encapsulation efficiency (Y(2)). Independent and dependent variables were analyzed with multiple regressions to establish a full-model second-order polynomial equation. F value was calculated to confirm the omission of insignificant parameters or interactions of parameters from the analysis to derive a reduced-model polynomial equation to predict the Y(1) and Y(2) of dacarbazine-loaded cubosomes. Pareto charts were also obtained to show the effects of X(1), X(2), and X(3) on Y(1) and Y(2). For Y(1), there was a model validated for more accurate prediction of response parameter by performing checkpoint analysis. The optimization process and Pareto charts were obtained automatically and they predicted the levels of independent parameters X(1), X(2), and X(3) (0.889794, 0.11886, and 0.56201, respectively) and minimized Y(1). The optimal process parameters (homogenization's speed = approximately 24,000 rpm, duration = 5.5 min, and temperature = 76 degrees C) led to the production of cubosomes with 85.6 nm in size and 16.7% in encapsulation efficiency. The Box-Behnken design proved to be a useful tool in the preparation and optimization of dacarbazine-loaded cubosomes. For encapsulation efficiency (Y(2)), further studies are needed to enhance the result and improve the model for such water-soluble drug encapsulation in cubosomes.

Formulation of dacarbazine-loaded cubosomes-part I: influence of formulation variables

The purpose of this study was to investigate the combined influence of three-level, three-factor variables on the formulation of dacarbazine (a water-soluble drug) loaded cubosomes. Box-Behnken design was used to obtain a second-order polynomial equation with interaction terms to predict response values. In this study, the selected and coded variables X(1), X(2), and X(3) representing the amount of monoolein, polymer, and drug as the independent variables, respectively. Fifteen runs of experiments were conducted, and the particle size (Y(1)) and encapsulation efficiency (Y(2)) were evaluated as dependent variables. We performed multiple regression to establish a full-model second-order polynomial equation relating independent and dependent variables. A second-order polynomial regression model was constructed for Y(1) and confirmed by performing checkpoint analysis. The optimization process and Pareto charts were obtained automatically, and they predicted the levels of independent coded variables X(1), X(2), and X(3) (-1, 0.53485, and -1, respectively) and minimized Y(1) while maximizing Y(2). These corresponded to a cubosome formulation made from 100 mg of monoolein, 107 mg of polymer, and 2 mg with average diameter of 104.7 nm and an encapsulation efficiency of 6.9%. The Box-Behnken design proved to be a useful tool to optimize the particle size of these drug-loaded cubosomes. For encapsulation efficiency (Y(2)), further studies are needed to identify appropriate regression model.

A specialized mitochondrial molecular chaperone system: a role in formation of Fe/S centers

Mitochondria contain a specialized system of molecular chaperones that plays a critical role in the biogenesis of Fe/S centers. This Hsp70:J-protein system shows many similarities to the system found in bacteria, but the precise role of neither chaperone system has been defined. However, evidence to date suggests an interaction with the scaffold protein on which a transient Fe/S center is assembled, and thus implies a role in either assembly of the center or its transfer to recipient proteins.

Jac1, a mitochondrial J-type chaperone, is involved in the biogenesis of Fe/S clusters in Saccharomyces cerevisiae

A minor Hsp70 chaperone of the mitochondrial matrix of Saccharomyces cerevisiae, Ssq1, is involved in the formation or repair of Fe/S clusters and/or mitochondrial iron metabolism. Here, we report evidence that Jac1, a J-type chaperone of the mitochondrial matrix, is the partner of Ssq1 in this process. Reduced activity of Jac1 results in a decrease in activity of Fe/S containing mitochondrial proteins and an accumulation of iron in mitochondria. Fe/S enzyme activities remain low in both jac1 and ssq1 mutant mitochondria even if normal mitochondrial iron levels are maintained. Therefore, the low activities observed are not solely due to oxidative damage caused by excess iron. Rather, these molecular chaperones likely play a direct role in the normal assembly process of Fe/S clusters.

Role of the mitochondrial Hsp70s, Ssc1 and Ssq1, in the maturation of Yfh1

The mitochondrial matrix of the yeast Saccharomyces cerevisiae contains two molecular chaperones of the Hsp70 class, Ssc1 and Ssq1. We report that Ssc1 and Ssq1 play sequential roles in the import and maturation of the yeast frataxin homologue (Yfh1). In vitro, radiolabeled Yfh1 was not imported into ssc1-3 mutant mitochondria, remaining in a protease-sensitive precursor form. As reported earlier, the Yfh1 intermediate form was only slowly processed to the mature form in Deltassq1 mitochondria (S. A. B. Knight, N. B. V. Sepuri, D. Pain, and A. Dancis, J. Biol. Chem. 273:18389-18393, 1998). However, the intermediate form in both wild-type and Deltassq1 mitochondria was entirely within the inner membrane, as it was resistant to digestion with protease after disruption of the outer membrane. Therefore, we conclude that Ssc1, which is present in mitochondria in approximately a 1,000-fold excess over Ssq1, is required for Yfh1 import into the matrix, while Ssq1 is necessary for the efficient processing of the intermediate to the mature form in isolated mitochondria. However, the steady-state level of mature Yfh1 in Deltassq1 mitochondria is approximately 75% of that found in wild-type mitochondria, indicating that this retardation in processing does not dramatically affect cellular concentrations. Therefore, Ssq1 likely has roles in addition to facilitating the processing of Yfh1. Twofold overexpression of Ssc1 partially suppresses the cold-sensitive growth phenotype of Deltassq1 cells, as well as the accumulation of mitochondrial iron and the defects in Fe/S enzyme activities normally found in Deltassq1 mitochondria. Deltassq1 mitochondria containing twofold-more Ssc1 efficiently converted the intermediate form of Yfh1 to the mature form. This correlation between the observed processing defect and suppression of in vivo phenotypes suggests that Ssc1 is able to carry out the functions of Ssq1, but only when present in approximately a 2,000-fold excess over normal levels of Ssq1.

Dual role of the mitochondrial chaperone Mdj1p in inheritance of mitochondrial DNA in yeast

Mdj1p, a homolog of the bacterial DnaJ chaperone protein, plays an essential role in the biogenesis of functional mitochondria in the yeast Saccharomyces cerevisiae. We analyzed the role of Mdj1p in the inheritance of mitochondrial DNA (mtDNA). Mitochondrial genomes were rapidly lost in a temperature-sensitive mdj1 mutant under nonpermissive conditions. The activity of mtDNA polymerase was severely reduced in the absence of functional Mdj1p at a nonpermissive temperature, demonstrating the dependence of the enzyme on Mdj1p. At a permissive temperature, the activity of mtDNA polymerase was not affected by the absence of Mdj1p. However, under these conditions, intact [rho(+)] genomes were rapidly converted to nonfunctional [rho(-)] genomes which were stably propagated in an mdj1 deletion strain. We propose that mtDNA polymerase depends on Mdj1p as a chaperone in order to acquire and/or maintain an active conformation at an elevated temperature. In addition, Mdj1p is required for the inheritance of intact mitochondrial genomes at a temperature supporting optimal growth; this second function appears to be unrelated to the function of Mdj1p in maintaining mtDNA polymerase activity.

Role of adenine nucleotides, molecular chaperones and chaperonins in stabilization of DnaA initiator protein of Escherichia coli

DnaA protein of Escherichia coli is a sequence-specific DNA binding protein required for the initiation of DNA replication from the chromosomal origin, oriC, and of several E. coli plasmids. At a moderate ionic strength, purified DnaA protein has a strong tendency to aggregate; the self-aggregate form is inactive in DNA replication. Binding of ATP or ADP to DnaA protein protected it from aggregation to maintain its replication activity. AMP or cyclic AMP had no protective effect. The molecular chaperone DnaK protected DnaA protein from aggregation with or without ATP. DnaJ and GrpE were not stimulatory. Chaperonins GroEL and GroES were also able to prevent aggregation but only in the presence of ATP. The studies presented here show that for DnaA protein to be active in the initiation of DNA replication, it must be prevented from forming a self-aggregate by the binding of adenine nucleotides, and/or by the action of molecular chaperones.

Interaction of the Escherichia coli DnaA protein with bacteriophage lambda DNA

Interaction of the Escherichia coli DnaA (replication initiator) protein with restriction fragments of phage lambda DNA demonstrated differential binding of DnaA along the whole lambda DNA. Interaction of DnaA with the lambda replication region (from the promoter pR to the origin of replication, orilambda) demonstrated a strong binding of DnaA to the region around the p(o) promoter where synthesis of a short antisense oop RNA is initiated. The four sequences protected by DnaA (two 9mers and two 5mers) are not related even to a relaxed DnaA box. The pattern of protection of these four sequences and the location of three DNase I hypersensitive sites in the lambda DNA r strand, together with results of mobility shift assays and electron microscopy studies, may indicate an interaction involving DnaA monomers bound to different DNA positions on one side of the helix and the formation of higher-order nucleoprotein structures. Therefore, it is tempting to suggest that DnaA, in addition to its activity in regulation of replication and transcription, could be considered as a factor which structures certain chromosomal regions.

Domains of DnaA protein involved in interaction with DnaB protein, and in unwinding the Escherichia coli chromosomal origin

DnaA protein of Escherichia coli is a sequence-specific DNA-binding protein required for the initiation of DNA replication from the chromosomal origin, oriC. It is also required for replication of several plasmids including pSC101, F, P-1, and R6K. A collection of monoclonal antibodies to DnaA protein has been produced and the primary epitopes recognized by them have been determined. These antibodies have also been examined for the ability to inhibit activities of DNA binding, ATP binding, unwinding of oriC, and replication of both an oriC plasmid, and an M13 single-stranded DNA with a proposed hairpin structure containing a DnaA protein-binding site. Replication of the latter DNA is dependent on DnaA protein by a mechanism termed ABC priming. These studies suggest regions of DnaA protein involved in interaction with DnaB protein, and in unwinding of oriC, or low-affinity binding of ATP.

Increasing neurofilament subunit NF-M expression reduces axonal NF-H, inhibits radial growth, and results in neurofilamentous accumulation in motor neurons

The carboxy-terminal tail domains of neurofilament subunits neurofilament NF-M and NF-H have been postulated to be responsible for the modulation of axonal caliber. To test how subunit composition affects caliber, transgenic mice were generated to increase axonal NF-M. Total neurofilament subunit content in motor and sensory axons remained essentially unchanged, but increases in NF-M were offset by proportionate decreases in both NF-H and axonal cross-sectional area. Increase in NF-M did not affect the level of phosphorylation of NF-H. This indicates that (a) in vivo NF-H and NF-M compete either for coassembly with a limiting amount of NF-L or as substrates for axonal transport, and (b) NF-H abundance is a primary determinant of axonal caliber. Despite inhibition of radial growth, increase in NF-M and reduction in axonal NF-H did not affect nearest neighbor spacing between neurofilaments, indicating that cross-bridging between nearest neighbors does not play a crucial role in radial growth. Increase in NF-M did not result in an overt phenotype or neuronal loss, although filamentous swellings in perikarya and proximal axons of motor neurons were frequently found.

The ClpX heat-shock protein of Escherichia coli, the ATP-dependent substrate specificity component of the ClpP-ClpX protease, is a novel molecular chaperone

All major classes of protein chaperones, including DnaK (the Hsp70 eukaryotic equivalent) and GroEL (the Hsp60 eukaryotic equivalent) have been found in Escherichia coli. Molecular chaperones enhance the yields of correctly folded polypeptides by preventing aggregation and even by disaggregating certain protein aggregates. Previously, we identified the ClpX heat-shock protein of E. coli because it enables the ClpP catalytic protease to degrade the bacteriophage lambda O replication protein. Here we report that ClpX alone possesses all the properties expected of a molecular chaperone protein. Specifically, it can protect the lambda O protein from heat-induced aggregation, disaggregate preformed lambda O aggregates, and even promote efficient binding of lambda O to its DNA recognition sequence. A lambda O-ClpX specific protein-protein interaction can be detected either by a modified ELISA assay or through the stimulation of ClpX's weak ATPase activity by lambda O. Unlike the behaviour of the major DnaK and GroEL chaperones, ClpX requires the presence of ATP or its non-hydrolysable analogue ATP-gamma-S for efficient interaction with other proteins including the protection of lambda O from aggregation. However, ClpX's ability to disaggregate lambda O aggregates requires hydrolysable ATP. We propose that the ClpX protein is a bona fide chaperone, whose biological role includes the maintenance of certain polypeptides in a form competent for proteolysis by the ClpP protease. Furthermore, our results suggest that the ClpX protein also performs typical chaperone protein functions independent of ClpP.

The requirement for molecular chaperones in lambda DNA replication is reduced by the mutation pi in lambda P gene, which weakens the interaction between lambda P protein and DnaB helicase

During the initiation of lambda DNA replication, the host DnaB helicase is complexed with phage lambda P protein in order to be properly positioned near the ori lambda-lambda O initiation complex. However, the lambda P-DnaB interaction inhibits the activities of DnaB. Thus, the concerted action of bacterial heat shock proteins, DnaK, DnaJ, and GrpE, is required to activate the helicase. Wild-type phage lambda cannot grow on the E. coli dnaB, dnaK, dnaJ, and grpE mutants. However, lambda phage with a mutation pi in the lambda P gene, is able to produce progeny in these mutants as well as in the wild-type bacteria. Purified mutant lambda pi protein reveals a much lower affinity to DnaB than wild-type lambda P, and the lambda pi-DnaB complex is unstable. Also, a very low concentration of DnaK protein is sufficient to activate the helicase in a replication system based on lambda dv dsDNA. In that system, the mutant DnaK756 protein, inactive in the lambda P-dependent replication, revealed its activity in the lambda pi-dependent reaction. The lambda O-lambda P-dependent replication system based on M13 ssDNA efficiently replicates DNA in the absence of any chaperone protein, unless lambda P is substituted by the lambda pi mutant protein. Data presented in this paper explain why lambda pi phage is able to grow on wild-type and dnaK756 bacteria.

DnaA protein directs the binding of DnaB protein in initiation of DNA replication in Escherichia coli

DnaA protein of Escherichia coli acts in the initiation of chromosomal replication to bind to sequences in the chromosomal origin. On binding, it promotes the assembly of other replication proteins that serve to prime DNA replication and assemble the replication apparatus for bidirectional replication fork movement. A collection of monoclonal antibodies to DnaA protein have been produced, one of which is described here, that interferes with the action of DnaA protein in promoting formation of a prepriming complex. On the analysis of this process, the antibody appears to interfere with the physical interaction between DnaA and DnaB protein in the DnaB.DnaC complex. Cross-linking studies confirm that DnaA and DnaB proteins interact directly. These results provide the first direct evidence that one of the roles of DnaA protein is to act as a site for binding of DnaB protein to the DNA and perhaps orients DnaB helicase to account for the directionality of replication fork movement.

Defective replication activity of a dominant-lethal dnaB gene product from Escherichia coli

dnaB protein of Escherichia coli is an essential replication protein. A missense mutant has been obtained which results in replacement of an arginine residue with cysteine at position 231 of the protein (P. Shrimankar, L. Shortle, and R. Maurer, unpublished data). This mutant displays a dominant-lethal phenotype in strains that are heterodiploid for dnaB. Biochemical analysis of the altered form of dnaB protein revealed that it was inactive in replication in several purified enzyme systems which involve specific and nonspecific primer formation on single-stranded DNAs, and in replication of plasmids containing the E. coli chromosomal origin. Inactivity in replication appeared to be due to its inability to bind to single-stranded DNA. The altered dnaB protein was inhibitory to the activity of wild type dnaB protein in replication by sequestering dnaC protein which is also required for replication. By contrast, it was not inhibitory to dnaB protein in priming of single-stranded DNA by primase in the absence of single-stranded DNA binding protein. Sequestering of dnaC protein into inactive complexes may relate to the dominant-lethal phenotype of this dnaB mutant.

Escherichia coli DnaJ and GrpE heat shock proteins jointly stimulate ATPase activity of DnaK

The products of the Escherichia coli dnaK, dnaJ, and grpE heat shock genes have been previously shown to be essential for bacteriophage lambda DNA replication at all temperatures and for bacterial survival under certain conditions. DnaK, the bacterial heat shock protein hsp70 analogue and putative chaperonin, possesses a weak ATPase activity. Previous work has shown that ATP hydrolysis allows the release of various polypeptides complexed with DnaK. Here we demonstrate that the ATPase activity of DnaK can be greatly stimulated, up to 50-fold, in the simultaneous presence of the DnaJ and GrpE heat shock proteins. The presence of either DnaJ or GrpE alone results in a slight stimulation of the ATPase activity of DnaK. The action of the DnaJ and GrpE proteins may be sequential, since the presence of DnaJ alone leads to an acceleration in the rate of hydrolysis of the DnaK-bound ATP. The presence of GrpE alone increases the rate of release of bound ATP or ADP without affecting the rate of hydrolysis. The stimulation of the ATPase activity of DnaK may contribute to its more efficient recycling, and it helps explain why mutations in dnaK, dnaJ, or grpE genes often exhibit similar pleiotropic phenotypes.

Regulatory properties of AMP deaminases from rat tissues

1. Phosphocellulose column chromatography under double gradient conditions (phosphate and KCl) revealed two forms of AMP deaminase in rat heart and brain and a single form in the liver and skeletal muscle. 2. Kinetically all purified AMP deaminases were classified into two categories: those, which elute from the column at lower KCl and Pi concentrations, display low S0.5 value are only moderately affected by MgATP, MgGTP and Pi; and those which elute at higher KCl and Pi concentrations, display high S0.5 values and are strongly regulated by allosteric effectors. 3. Physiological significance of the occurrence of two kinetic forms of AMP deaminase in some tissues is discussed.

Regulation of platelet AMP deaminase activity in situ

The regulation of platelet AMP deaminase activity by ATP, GTP and phosphate was studied in human platelets in situ, and in vitro after partial purification. In intact platelets, a similar 50% decrease in cytosolic ATP was induced by either glucose starvation or treatment with H2O2. During starvation, AMP deaminase was in the inhibited state, as ATP consumption was mostly balanced by the accumulation of AMP. During H2O2 treatment, however, the enzyme was in the stimulated state, as the AMP formed was almost completely deaminated to IMP. Cytosolic GTP fell by 40-50% in both starvation and H2O2 treatment. In contrast, intracellular phosphate was 4-5-fold higher in starved than in H2O2-treated cells. These data point to phosphate as the main regulator of AMP deaminase activity in situ. This conclusion was verified by kinetic analysis of partially purified AMP deaminase. At near-physiological concentrations of MgATP, MgGTP and phosphate, the S0.5 (substrate half-saturation constant) for AMP was 0.35 mM. Half-maximal stimulation by MgATP occurred at a concn. between 2 and 3 mM. This stimulation was antagonized by the inhibitory effects of phosphate (IC50 = 2.0 mM) and MgGTP (IC50 = 0.2-0.3 mM), which acted in synergism (IC50 is the concentration causing 50% inhibition). We conclude that the difference in adenylate catabolism between starved and H2O2-treated platelets is due to the distinct phosphate concentrations. During starvation, refeeding and H2O2 treatment, the values of the adenylate charge and the phosphorylation potential were kept closely co-ordinated, which may be effected by AMP deaminase.