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Biomedical subjects

M Geyer

Publications and source records attributed to M Geyer.

At least 19 recordsLinked to original sources
PubMed2001

A natural variability in the proline-rich motif of Nef modulates HIV-1 replication in primary T cells.

In the infected host, the Nef protein of HIV/SIV is required for high viral loads and thus disease progression. Recent evidence indicates that Nef enhances replication in the T cell compartment after the virus is transmitted from dendritic cells (DC). The underlying mechanism, however, is not clear. Here, we report that a natural variability in the proline-rich motif (R71T) profoundly modulated Nef-stimulated viral replication in primary T cells of immature dendritic cell/T cell cocultures. Whereas both Nef variants (R/T-Nef) downregulated CD4, only the isoform supporting viral replication (R-Nef) efficiently interacted with signaling molecules of the T cell receptor (TCR) environment and stimulated cellular activation. Structural analysis suggested that the R to T conversion induces conformational changes, altering the flexibility of the loop containing the PxxP motif and hence its ability to bind cellular partners. Our report suggests that functionally and conformationally distinct Nef isoforms modulate HIV replication on the interaction level with the TCR-signaling environment once the virus enters the T cell compartment.

Amino Acid Motifs↗
PubMed2001

Domain assembly, surface accessibility and sequence conservation in full length HIV-1 Nef.

The accessory Nef protein from human and simian immunodeficiency viruses is critical for efficient viral replication and pathogenesis. Here we present an assembly of the full length structure of HIV-1 Nef, allele NL4-3, based on the previously solved anchor and core domain structures. The center part of the 33 residue encompassing flexible loop at the C-terminus of Nef, involved in Nef internalization and CD4 endocytosis, has been modelled. The degree of sequence conservation in HIV-1 Nef proteins was determined using a total of 186 different strains from five different subtypes. The sequence conservation has been correlated with the accessible surface area and with secondary structure features for individual residues. The high amount of flexible regions in Nef accounts for the large surface and the multiple interaction sites the protein exhibits.

Alleles↗
PubMed2001

The Rev/Rex homolog HERV-K cORF multimerizes via a C-terminal domain.

Expression of human endogenous retrovirus K (HERV-K) is associated with germ-cell neoplasia. HERV-K encodes a protein of the Rev/Rex family, cORF, that supports cellular transformation and binds the promyelocytic leukemia zinc finger (PLZF) protein implicated in spermatogenesis. Rev/Rex function invariably depends on multimerization. Here we show that cORF likewise self-associates to form higher-order oligomers. Amino acids (aa) 47-87 in cORF are sufficient, aa 75-87 essential for self-association. Consistently, this domain is predicted to form a hydrophobic alpha-helix that may represent an oligomerization interface. The existence of a dimerization-competent cORF mutant lacking PLZF-binding activity (cORF47-87) suggests a way of dominant negative inhibition of the proposed tumor susceptibility factor cORF.

Dimerization↗
PubMed2001

[Psychiatric problems in the elderly--standardization of the Symptom Check List SCL-90-R in patients over 60 years of age].

In the following article, data of the symptom checklist SCL-90-R (Derogatis 1986) for elderly people are introduced, including an estimation of the controlling factors on psychological complaints in old age. The representative sample is based on 394 persons aged 61 to 96; their psychological complaints have been studied with respect to SCL-90-R. Evidently elderly people did not state an increasing load on psychological complaints, but a different structure of psychological symptoms. Therefore with increasing age the scales "Somatization", "Obsessive-compulsive" and "Phobic anxiety" increase, while "Interpersonal sensitivity", "Anger--hostility" and "Paranoid ideation" are decreasing. Within that frame, elderly females report increasing symptomatic load compared to elderly males. Furthermore, aspects of social support and health-related attitudes were found to be important predictors of psychological complaints in old age.

Aged↗
PubMed2001

Solution NMR structure of the cold-shock protein from the hyperthermophilic bacterium Thermotoga maritima.

Cold-shock proteins (Csps) are a subgroup of the cold-induced proteins preferentially expressed in bacteria and other organisms on reduction of the growth temperature below the physiological temperature. They are related to the cold-shock domain found in eukaryotes and are some of the most conserved proteins known. Their exact function is still not known, but translational regulation, possibly via RNA chaperoning, has been discussed. Here we present the structure of a hyperthermophilic member of the Csp family. The NMR solution structure of TmCsp from Thermotoga maritima, the hyperthermophilic member of this class of proteins, was solved on the basis of 1015 conformational constraints. It contains five beta strands combined in two antiparallel beta sheets making up a beta barrel structure, in which beta strands 1-4 are arranged in a Greek-key topology. The side chain of R2, which is exclusively found in thermophilic members of the Csp family, probably participates in a peripheral ion cluster involving residues D20, R2, E47 and K63, suggesting that the thermostability of TmCsp is based on the peripheral ion cluster around the side chain of R2.

Amino Acid Sequence↗
PubMed2001

Negative factor from SIV binds to the catalytic subunit of the V-ATPase to internalize CD4 and to increase viral infectivity.

The accessory protein negative factor (Nef) from human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) is required for optimal viral infectivity and the progression to acquired immunodeficiency syndrome (AIDS). Nef interacts with the endocytic machinery, resulting in the down-regulation of cluster of differentiation antigen 4 (CD4) and major histocompatibility complex class I (MHCI) molecules on the surface of infected cells. Mutations in the C-terminal flexible loop of Nef result in a lower rate of internalization by this viral protein. However, no loop-dependent binding of Nef to adaptor protein-2 (AP-2), which is the adaptor protein complex that is required for the internalization of proteins from the plasma membrane, could be demonstrated. In this study we investigated the relevance of different motifs in Nef from SIV(mac239) for its internalization, CD4 down-regulation, binding to components of the trafficking machinery, and viral infectivity. Our data suggest that the binding of Nef to the catalytic subunit H of the vacuolar membrane ATPase (V-ATPase) facilitates its internalization. This binding depends on the integrity of the whole flexible loop. Subsequent studies on Nef mutant viruses revealed that the flexible loop is essential for optimal viral infectivity. Therefore, our data demonstrate how Nef contacts the endocytic machinery in the absence of its direct binding to AP-2 and suggest an important role for subunit H of the V-ATPase in viral infectivity.

Adaptor Proteins, Vesicular Transport↗
PubMed2001

Structure--function relationships in HIV-1 Nef.

The accessory Nef protein of HIV and SIV is essential for viral pathogenesis, yet it is perplexing in its multitude of molecular functions. In this review we analyse the structure-function relationships of motifs recently proposed to play roles in aspects of Nef modification, signalling and trafficking, and thereby to impinge on the ability of the virus to survive in, and to manipulate, its cellular host. Based on the full-length structure assembly of HIV Nef, we correlate surface accessibility with secondary structure elements and sequence conservation. Motifs involved in Nef-mediated CD4 and MHC I downregulation are located in flexible regions of Nef, suggesting that the formation of the transient trafficking complexes involved in these processes depends on the recognition of primary sequences. In contrast, the interaction sites for signalling molecules that contain SH3 domains or the p21-activated kinases are associated with the well folded core domain, suggesting the recognition of highly structured protein surfaces.

Amino Acid Motifs↗
PubMed2001

Analysis of ankyrin repeats reveals how a single point mutation in RFXANK results in bare lymphocyte syndrome.

Ankyrin repeats are well-known structural modules that mediate interactions between a wide spectrum of proteins. The regulatory factor X with ankyrin repeats (RFXANK) is a subunit of a tripartite RFX complex that assembles on promoters of major histocompatibility complex class II (MHC II) genes. Although it is known that RFXANK plays a central role in the nucleation of RFX, it was not clear how its ankyrin repeats mediate the interactions within the complex and with other proteins. To answer this question, we modeled the RFXANK protein and determined the variable residues of the ankyrin repeats that should contact other proteins. Site-directed alanine mutagenesis of these residues together with in vitro and in vivo binding studies elucidated how RFXAP and CIITA, which simultaneously interact with RFXANK in vivo, bind to two opposite faces of its ankyrin repeats. Moreover, the binding of RFXAP requires two separate surfaces on RFXANK. One of them, which is located in the ankyrin groove, is severely affected in the FZA patient with the bare lymphocyte syndrome. This genetic disease blocks the expression of MHC II molecules on the surface of B cells. By pinpointing the interacting residues of the ankyrin repeats of RFXANK, the mechanism of this subtype of severe combined immunodeficiency was revealed.

Amino Acid Sequence↗
PubMed2001

[Central relationship patterns in comparison with different objects].

In the present study the Relationship Episode Paradigm Interviews of 70 female patients with different psychoneurotic diseases were analysed with respect to object-specific patterns with the CCRT method. The most frequent categories are the same in all relationship episodes and in subsamples of relationship episodes with mother and father. These categories are also predominant in episodes with women and men. Relationship episodes with mother do not differ from episodes with father, and relationship episodes with women are not different from episodes with men. But there are substantial differences in relationship episodes with the mother and women and between episodes with the father and men. Patients recount much more positive relationship patterns with women and men than with their parents. This could be understood as a hint of interpersonal resources.

Adult↗
PubMed2000

[Utilization of medical services and medication intake of patients over 60 in Germany--health related, social structure related, socio-demographic and subjective factors].

In a community sample of 394 elderly aged 61 years and older from East and West Germany, diseases, contacts with general practitioners and specialists, the use of medicine, attitudes regarding health and illness, the subjective health, psychic problems, social support, social integration, social burden, and socio-demographic variables were assessed. Based on these data the determinants for the contact of physicians and the use of medicine were analyzed. The results confirmed the frequency of multimorbidity in the elderly; on average we found three different diseases at the same time for each person. In nearly 10% of the sample we found seven diagnoses existing at the same time. 88% had contact with a general practitioner at least once a year, 97% had contact either with a general practitioner or with a specialist once a year. 55.8% took at least one medicine each day. The number of diseases existing at the same time was the most determining variable for the contact of physicians and the use of medicine. Furthermore, the elderly had more contact with physicians and took more medicine if they thought they were susceptible to diseases in a high degree, and if they rated their own health as poor. Fewer contacts with physicians and a lower use of medicine were found in those elderly that rated health behavior as little useful, that had low control beliefs regarding their own health, and that experienced only a low degree of health-related limitations in their everyday life. Furthermore, we found a higher use of medicine if there was little social support. There were no significant age-related or sex-related differences regarding the contact of practitioners or the use of medicine.

Aged↗
PubMed2000

[Illness-coping in a population-based representative sample. Situational, sociodemographic and social influences].

In spite of the considerable volume of current coping research there is a noticeable lack of studies based on large representative samples. In this study a sample of 2179 subjects of 16 to 96 years of age that was representative of the entire population of Germany, was asked as to how they now cope, how they have coped in the past or how they would cope with: 1. an existing illness, 2. a past illness and 3. an imagined (non-existent) illness. The instrument used was the questionnaire version of the "Berner Bewältigungsformen" (BEFO), a coping questionnaire with 28 systematically derived coping dimensions that are defined independently of the usual empirical-topographical dimensions (behavioural, cognitive and emotional) of the type of illness. The enquiry was concerned with the influence of varying situational (proximity of illness, subjective evaluation of personal health, psychological symptoms), socio-demographic (age, gender) and social (social support) variables on the choice of coping mechanisms. The results showed that each of these factors influences the repertoire of coping mechanisms to varying degrees. This systematic variability in a representative sample should be taken into account in any evaluation of coping with illness in clinical sub-groups.

Adaptation, Psychological↗
PubMed2000

Interactions between equine cyclin T1, Tat, and TAR are disrupted by a leucine-to-valine substitution found in human cyclin T1.

Transcriptional transactivators (Tat) from human immunodeficiency and equine infectious anemia viruses (HIV and EIAV) interact with their transactivation response elements (TAR) to increase the rates of viral transcription. Whereas the human cyclin T1 is required for the binding of Tat to TAR from HIV, it is unknown how Tat from EIAV interacts with its TAR. Furthermore, Tat from EIAV functions in equine and canine cells but not in human cells. In this study, we present sequences of cyclins T1 from horse and dog and demonstrate that their N-terminal 300 residues rescue the transactivation of Tat from EIAV in human cells. Although human and equine cyclins T1 bind to this Tat, only the equine cyclin T1 supports the binding of Tat to TAR from EIAV. Finally, a reciprocal exchange of the valine for the leucine at position 29 in human and equine cyclins T1, respectively, renders the human cyclin T1 active and the equine cyclin T1 inactive for Tat transactivation from EIAV. Thus, the collaboration between a specific cyclin T1 and Tat for their high-affinity interaction with TAR is a common theme of lentiviral transactivation.

Amino Acid Sequence↗
PubMed2000

p21-activated kinase 1 plays a critical role in cellular activation by Nef.

The activation of Nef-associated kinase (NAK) by Nef from human and simian immunodeficiency viruses is critical for efficient viral replication and pathogenesis. This induction occurs via the guanine nucleotide exchange factor Vav and the small GTPases Rac1 and Cdc42. In this study, we identified NAK as p21-activated kinase 1 (PAK1). PAK1 bound to Nef in vitro and in vivo. Moreover, the induction of cytoskeletal rearrangements such as the formation of trichopodia, the activation of Jun N-terminal kinase, and the increase of viral production were blocked by an inhibitory peptide that targets the kinase activity of PAK1 (PAK1 83-149). These results identify NAK as PAK1 and emphasize the central role its kinase activity plays in cytoskeletal rearrangements and cellular signaling by Nef.

Animals↗
PubMed2000

[Not Available].

It may be possible to identify elements of psychosomatic/psychotherapeutic pri-mary care in the Federal Republic of Germany and the former German Democratic Republic by comparing the current state of basic psychosomatic care (BPSC) in the eastern and western part of Berlin. 278 Berlin patients with psychosocial problems were recruited 1995 for a basic documentation system of the BPSC in connection with a project supported by the Federal Ministry for Health at the Berlin Center. Their data were compared with re-gard to diagnostic and therapeutic measures applied in the eastern and western part of Berlin. Furthermore, 617 questionnaires on basic psychosomatic care were filled out by physicians in private practice in both parts of the city in 1994. Despite the identical or lower assessment of their patients* biopsychosocial stress, East Berlin physicians take considerably more therapeutic measures than their collea-gues in West Berlin. There are only minor differences between physicians from the eastern and western part of the city despite variances in the training and advanced training systems for BPSC. The possible causes are discussed.

Diagnosis↗
PubMed2000

[Method of plan formulation: first German language rehabilitation study of the Joseph Weiss "control mastery theory"].

The paper gives a survey of the "Control Mastery Theory" (CMT) of Joseph Weiss. CMT is a cognitive-affective, psychoanalytic theory of the psychotherapeutic process. The San Francisco Psychotherapy Research Group empirically investigated und confirmed several concepts of the CMT. Some research results are summarized and the "Plan Formulation Method" is described in detail. The results of the first German reliability study applying the plan formulation method on the case "Amalie" show that the method can be used reliably for research purposes outside the USA.

Adult↗
PubMed1999

Nucleotide-binding characteristics of human guanylate-binding protein 1 (hGBP1) and identification of the third GTP-binding motif.

hGBP1 is a GTPase with antiviral activity encoded by an interferon- activated human gene. Specific binding of hGBP1 to guanine nucleotides has been established although only two classical GTP-binding motifs were found in its primary sequence. The unique position of hGBP1 amongst known GTPases is further demonstrated by the hydrolysis of GTP to GDP and GMP. Although subsequent cleavage of orthophosphates rather than pyrophosphate was demonstrated, GDP coming from bulk solution cannot serve as a substrate. The relation of guanine nucleotide binding and hydrolysis to the antiviral function of hGBP1 is unknown. Here we show similar binding affinities for all three guanine nucleotides and the ability of both products, GDP and GMP, to compete with GTP binding. Fluorimetry and isothermal titration calorimetry were applied to prove that only one nucleotide binding site is present in hGBP1. Furthermore, we identified the third canonical GTP-binding motif and verified its role in nucleotide recognition by mutational analysis. The high guanine nucleotide dissociation rates measured by stopped-flow kinetics are responsible for the weak affinities to hGBP1 when compared to other GTPases like Ras or Galpha. By means of fluorescence and NMR spectroscopy it is demonstrated that aluminium fluoride forms a complex with hGBP1 only in the GDP state, presumably mimicking the transition state of GTP hydrolysis. Tentatively, the involvement of a GAP domain in hGBP1 in GTP hydrolysis is suggested. These results will serve as a basis for the determination of the differential biological functions of the three nucleotide states and for the elucidation of the unique mechanism of nucleotide hydrolysis catalysed by hGBP1.

Aluminum Compounds↗