Characterization of a Ca(2+)-binding site in human annexin II by site-directed mutagenesis

Annexin II, a major cytoplasmic substrate of the src tyrosine kinase, is a member of the annexin family of Ca2+/phospholipid-binding proteins. It is composed of a short N-terminal tail (30 residues) followed by four so-called annexin repeats (each 70-80 residues in length) which share sequence homologies and are thought to form (a) new type(s) of Ca(2+)-binding site(s). We have produced wild-type and site specifically mutated annexin II molecules to compare their structure and biochemistry. The recombinant wild-type annexin II displays biochemical and spectroscopical properties resembling those of the authentic protein purified from mammalian cells. In particular, it shows the Ca(2+)-induced blue shift in fluorescence emission which is typical for this annexin. Replacement of the single tryptophan in annexin II (Trp-212) by a phenylalanine abolishes the fluorescence signal and allows the unambiguous assignment of the Ca(2+)-sensitive spectroscopic properties to Trp-212. This residue is located in the third annexin repeat in a highly conserved stretch of 17 amino acids which are also found in the other repeats and known as the endonexin fold. To study the precise architecture of the Ca2+ site which must reside in close proximity to Trp-212, we changed several residues of the endonexin fold in repeat 3 by site-directed mutagenesis. An analysis of these mutants by fluorescence spectroscopy and Ca(2+)-dependent phospholipid binding reveals that Gly-206 and Thr-207 seem indispensible for a correct folding of this Ca(2+)-binding site.

Characterization of a discontinuous epitope on annexin II by site-directed mutagenesis

Recombinant annexin II mutants were generated to identify amino acids involved in the formation of the discontinuous epitope of the monoclonal antibody H28. Analysis of the various mutant proteins by immunoblotting and enzyme-linked immunosorbent assay revealed that residues Lys27, Arg62, Glu65, and Arg67 are indispensable for H28 reactivity. Residues in equivalent positions are also in close proximity in the recently determined X-ray structure of annexin V, a different member of the same family of Ca2+/lipid-binding proteins. Thus annexins II and V show a similar three-dimensional folding in this region of the molecule. Consequently, the Ca2+ binding sites and the residues phosphorylated by pp60src (Tyr23) and protein kinase C (Ser25) most likely reside on opposite sides of the annexin II molecule.

Primary structure of human, chicken, and Xenopus laevis p11, a cellular ligand of the Src-kinase substrate, annexin II

The p11 protein is a member of the S-100 family of Ca(2+)-binding proteins and serves within the cell as a ligand of the tyrosine kinase substrate, annexin II. To obtain more structural information on this molecule, we have isolated and characterized p11 cDNA clones from several different species. A comparison of the deduced amino acid (aa) sequences reveals that mammalian and avian p11 are highly similar (at least 90% identical at the aa level), whereas p11 from Xenopus laevis shows a considerable degree of sequence variation (the aa sequence identity drops to approx. 60% when compared to mammalian or chicken p11). Interestingly, the C-terminal 18 aa, which are unique to p11 within the S-100 family, show a relatively high conservation among species. This high evolutionary conservation is in line with a structurally and/or functionally important role of this C terminus, e.g., in annexin II binding.

Reduction of nocturnal diuresis and natriuresis during treatment of obstructive sleep apnea (OSA) with nasal continuous positive air pressure (nCPAP) correlates to cGMP excretion

In ten patients with severe obstructive sleep apnea (OSA) profound changes in renal function could be demonstrated at night during nCPAP therapy. Natriuresis and diuresis decreased by about 50% while creatinine excretion rate and urinary osmolality did not change. We found parallel changes in the excretion of ANP's second messenger cyclic guanosine monophosphate (cGMP) in a dose-response-related manner to natriuresis respectively diuresis. These data are in agreement with recently demonstrated decrease of nocturnal plasma levels of atrial natriuretic peptide (ANP) during nCPAP therapy in apneic patients. This may be an indicator for an increased cardiac volume load during obstructive apnea. The decrease of diuresis, natriuresis and cGMP excretion demonstrate the beneficial effects of nCPAP treatment on the cardiovascular system. Therefore measurements of cGMP excretion may be a useful parameter to assess the cardiovascular function of apneic patients before and during treatment.

Age, cardiovascular risk factors and coronary heart disease as determinants of platelet function in men. A multivariate approach

Older age, the cardiovascular risk factors and arteriosclerosis have been reported to be associated with stimulated platelet function. To evaluate the relative importance of these factors in determining platelet function, a cross-sectional multivariate study in 191 men, 113 healthy subjects and 78 patients with angiographically documented coronary heart disease, was performed. In healthy subjects, stepwise multiple linear regression identified age to be a major determinant of platelet aggregability. After induction with both ADP and collagen the platelet aggregatory response markedly increased with age. In the patients, platelet function was not age dependent. In multivariate analysis of variance, neither smoking status nor hypercholesterolemia (greater than or equal to 240 mg/dl) were determinants of platelet function in either group. An increase in systolic blood pressure was associated with slightly more inhibited ADP induced aggregation in both healthy subjects and patients with coronary heart disease. In patients compared to healthy subjects, aggregation after induction with ADP and collagen was markedly enhanced and the in vitro formation of thromboxane after collagen stimulation increased. Thus, by multivariate analysis, age and the presence or absence of coronary heart disease were found to be major determinants of platelet function. In contrast, the cardiovascular risk factors smoking, hypercholesterolemia and hypertension were associated with only minor or no alterations of platelet function.

Modulation of keratin intermediate filament assembly by single amino acid exchanges in the consensus sequence at the C-terminal end of the rod domain

All known intermediate filament (IF) proteins display -8 -4 -1 a consensus sequence TYRKLLEGE at the carboxyl end of the rod domain. To analyse the contribution of this sequence to the formation of IF we have changed two of the invariant positions of this motif by site-directed mutagenesis. We produced three mutant keratins, each containing a single point mutation. Tyrosine at position -8 was changed to alanine in keratin K8 (K8Y----A-8) and keratin K18 (K18Y----A-8) and leucine at position -4 was changed to glycine in keratin K18 (K18L----G-4). Mutant keratins were expressed in Escherichia coli, purified and analysed for their filament-forming capacity in vitro using either the complementary wild-type keratin or the corresponding mixture of mutant keratins. In standard filament buffer (50 mM Tris-HCl, pH7.5), assembly involving any of the mutants leads to large electron-dense aggregates instead of normal IF. In order to explain this effect, we studied the process of filament formation in more detail. Whereas the formation of tetramers in buffers containing 4M urea is unaffected, the elongation process seems slowed down. In buffer of lower ionic strength (10 mM Tris-HCl, pH7.5) mutant keratins K8Y----A-8 plus K18Y----A-8 become able to form long filaments, although short filaments and protofilamentous material are still detected. The filaments formed differ from normal keratin IF by their remarkable tendency to aggregate into thick cables. Assemblies involving K18L----G-4 can only form short IF lengths. The dense aggregates formed in standard filament buffer are able to dissociate into IF and their fragments upon dialysis into 10 mM Tris-HCl, pH7.5. The results show that the consensus sequence is needed for IF formation under normal conditions and that already one mutation per heterodimer affects the assembly.

[Sleep-related respiratory disorders and coronary heart disease]

A review of the literature shows that more than 50% of examined patients suffering from coronary heart disease were also suffering from sleep-related apnea. We were able to diagnose a pathological sleep apnea in 9 out of 25 patients (36%) suffering from an angiographically confirmed coronary 2-vessel and 3-vessel disorder. Patients with this combination--this is the hypothesis derived from our study--are at risk due to nocturnal apnea-induced myocardial ischaemia and rhythmic disorders. In 15 patients with sleep apnea and coronary heart disease or small vessel disease, nocturnal polysomnography was conducted, in parallel a 6-channel ECG was recorded. The apnea index (second night) was on the average 33 phases/h, the maximal duration of an apnea phases being 120 seconds. The minimal blood gas saturation recorded during sleep was between 46 and 89% (median 76.0%). In 4 of the 15 patients it was possible to confirm myocardial ischaemia (correlated via REM and also via NREM) with a maximum duration of 60 seconds, mainly during the phases of maximal apnea activity and blood gas desaturation. On comparing the ventricular arrhythmias waking/sleep, the Lown class did not change in 12 patients; there was deterioration in 2 patients and in one patient a qualitative improvement during the sleep phase. Patients suffering from sleep-related respiratory disorders and coronary heart disease are at cardiac risk, the more so since long-lasting apneas can lead to conditions of hypoxia at the heart in pre-existing changes in the coronary arteries, restricted coronary reserves and reduced tolerance to hypoxia. Such hypoxia can in turn induce enhanced electrical instability and a disturbance of the contractile function.

Purification and physical properties of nematode mini-titins and their relation to twitchin

We have isolated mini-titin from the nematodes Ascaris lumbricoides and Caenorhabditis elegans under native conditions using a modification in the procedure to prepare this protein from insect muscle. The proteins have an apparent molecular weight of 600,000 and appear in oriented specimens as flexible thin rods with a length around 240–250 nm. The circular dichroism spectrum of the Ascaris protein is dominated by beta-structure. The proteins react with antibodies to insect mini-titin and also with antibodies raised against peptides contained in the sequence predicted for twitchin, the product of the Caenorhabditis elegans unc-22 gene. Antibodies to insect mini-titin decorate the body musculature as well as the pharynx of wild-type C. elegans in immunofluorescence microscopy. In the twitchin mutant E66 only the pharynx is decorated. We conclude that the mini-titins of invertebrate muscles defined earlier by ultrastructural criteria are very likely to be twitchins, i.e. molecules necessary for normal muscle contraction. We discuss the molecular properties of the proteins in the light of the sequence established for twitchin.

Versatile controlling system for cryopreparation techniques in electron microscopy

A new setup for freeze-substitution and a versatile controlling system has been developed. Our goal was to build a simple system allowing precise control of the physical parameters of freeze-substitution experiments to learn more about their influences on the cellular ultrastructure and immunoreactivity of macromolecules. An improved apparatus for freeze-substitution, based on liquid nitrogen cooling, and a universal software for controlling the complex preparation protocols from cryofixation to final polymerization are described. This controlling system has the following advantages: it allows precise control and registration of temperature profiles, reconstruction of each individual step of previous experiments, and optimization of working conditions. The setup of the freeze-substitution apparatus is designed to run many different substitution media in parallel; freeze-substitution (cryostat), embedding (working platform), and polymerization are carried out at separate places; therefore, more experiments can be done simultaneously. The ergonomic working platform allows exchange of media at controlled temperature and easy handling; survey of the temperature in individual tubes is possible, and the system is protected from water condensation and uncontrolled warming by the deep freezer.

Characterization of the cell-cycle-regulated protein calcyclin from Ehrlich ascites tumor cells. Identification of two binding proteins obtained by Ca2(+)-dependent affinity chromatography

The nearly complete amino acid sequence obtained for murine calcyclin from Ehrlich ascites tumor cells reveals a very strong similarity with the rat and human sequences previously deduced from corresponding cDNA clones. While mouse and rat calcyclins are identical, the human protein shows at three positions a conservative amino acid replacement. Using a mouse calcyclin affinity matrix, two proteins with molecular masses of about 36 kDa have been purified from Ehrlich ascites tumor cells. The interaction between these two proteins and the immobilized calcyclin is strictly Ca2(+)-dependent. Immunological criteria and partial sequence data identify the two calcyclin-binding proteins as the phospholipid-binding protein annexin II (p36) and the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase. These observations suggest that calcyclin may exert its physiological function by a Ca2(+)-dependent interaction with cellular targets, e.g. annexin II or glyceraldehyde-3-phosphate dehydrogenase.

Dendritic accessory cells derived from rat bone marrow precursors under chemically defined conditions in vitro belong to the myeloid lineage

Serum-free conditions have been developed to differentiate dendritic cells from a non-adherent fraction of rat bone marrow precursors by action of the multipotential and macrophage colony-stimulating factors further supplemented with linoleic acid, vitamin E, and vitamin D3. Accessory activity was demonstrated by the high potency of the dendritic cells to stimulate autologous T cell proliferation, whereas such cells were negative for Fc receptor-dependent phagocytosis, a characteristic macrophage feature. While the dendritic cells were weakly positive for alpha-naphtylbutyrate esterase, they strongly expressed RT.1 class II antigens. Apparently, these cells represent a more differentiated phenotype since they expressed the nuclear A/C lamins. By addition of serum to the cultures, the dendritic cells developed into macrophages, which were also lamin A/C-positive as well as strongly positive for alpha-naphtylbutyrate esterase. Thus, these dendritic cells belong to the myeloid lineage, and it appears as if serum factor(s) control differentiation at a mature level. Suitable conditions could also be established for large-scale cultures of dendritic cells, which would be useful for applications requiring higher numbers of cells.

High molecular weight components are main constituents of Mallory bodies isolated with a fluorescence activated cell sorter

Mallory bodies (MBs) are cytoplasmic filamentous aggregates containing cytokeratin (CK) material. They occur in hepatocytes of patients with alcoholic liver disease (i.e., alcoholic hepatitis) and can also be induced experimentally in mice by chronic griseofulvin intoxication. To further investigate components and mechanisms involved in MB formation, a new method for MB purification was established. MBs present in a liver homogenate of griseofulvin-fed mice were labeled with a murine monoclonal antibody specific for MBs and a second fluorescein isothiocyanate-conjugated (anti-mouse IgG and IgM) antibody and subsequently isolated by two sequential sorting procedures using a fluorescence activated cell sorter (FACS). Purity of MB isolates was over 90% as revealed by computer analysis of sorting signals and fluorescence and electron microscopy. Electrophoretic separation on sodium dodecyl sulfate-polyacrylamide gels revealed three MB-related polypeptides with apparent molecular masses of 48, 55, and 65 kilodaltons but most of the highly purified MB material did not enter the gel or remained at the interphase between stacking and resolving gels. Western blotting with CK-specific antibodies showed the presence of CK epitopes in the high molecular weight MB material, which has a similar amino acid composition as normal liver CKs. These results establish that very high molecular weight material is the main constituent of MBs and suggest that a post-translational modification of CKs by covalent crosslinks is a principal mechanism of MB pathogenesis.

Influence of antihypertensive drug therapy on sleep pattern and sleep apnea activity

Sleep apnea, which affects 10% of men in the mean age group, is a common illness, and arterial hypertension one of its early symptoms. For the large group of, mainly young, patients with mild to moderate sleep apnea and arterial hypertension it is important to have a drug treatment available which will effectively control blood pressure without exacerbating symptoms of sleep apnea. We studied the effects of antihypertensive agents on blood pressure, sleep and sleep apnea in a randomized double-blind study of 24 patients with a sleep apnea activity of more than 10 apnea phases per hour of sleep and arterial hypertension with diastolic blood pressure values in the sitting position greater than or equal to 95 mm Hg. Mean age was 51 (range: 33-69) years, mean body mass index 31.4 (24.9-40.6) kg/m2. The study protocol envisaged two baseline measurements in the sleep laboratory, after which the medication was administered for 8 days. On the last 2 days of the treatment, polysomnographic leads were once again recorded in the sleep laboratory. The patients received either the beta-blocker metoprolol (1 x 100 mg/day) or the angiotensin-converting enzyme inhibitor cilazapril (1 x 2.5 mg/day). Systolic and diastolic blood pressure were decreased by both substances as expected. Total sleep time was 358 (233-425) min vs. 332 (255-383) min in the metoprolol group and 368 (295-424) min vs. 341 (265-434) min in the cilazapril group which is statistically not different between the two groups nor between the proportions of non-REM and REM sleep.(ABSTRACT TRUNCATED AT 250 WORDS)

Vimentin expression appears to be associated with poor prognosis in node-negative ductal NOS breast carcinomas

Vimentin expression in tumors from 83 node-negative and 112 node-positive patients with infiltrative ductal not otherwise specified (NOS) breast carcinomas has been compared with 5-year survival. For node-negative, but not for node-positive patients, there was a significant inverse relation between vimentin expression and survival. Five-year survival of node-negative patients with vimentin-positive tumors was significantly worse compared with vimentin-negative tumors (P less than 0.0001). In the node-negative group, only 36% of patients with vimentin-positive tumors but 82% of patients with vimentin-negative tumors survived 5 years. Tumors of all eight node-negative patients with ductal NOS cancer who died in the first 27 months expressed vimentin. Multivariate analysis of the node-negative group showed a strong correlation of vimentin expression and overall survival, but weak and not significant correlation between histologic grade or size and overall survival at 5 years. Thus vimentin expression seems to be a strong indicator of poor prognosis in node-negative ductal NOS breast carcinomas.

Protein-protein recognition via short amphiphilic helices; a mutational analysis of the binding site of annexin II for p11

Annexin II (p36) interacts with its ligand p11 via the short stretch of 12 amino acids (Ac-S-T-V-H-E-I-L-C-K-L-S-L) situated at the N-terminus. We have now synthesized some 37 tetradecapeptides, which differ from the original p11 binding sequence (Ac1-14) by single amino acid substitutions. The relative affinity of each peptide for p11 was determined by fluorescence spectroscopy using a competitive binding assay. The binding behaviour of the different peptides confirms the model of an amphiphilic alpha-helix induced upon binding to p11. The apparent affinities delta delta Gbind of the mutant peptides revealed that the N-acetyl group of serine 1 and the hydrophobic side chains at positions 3, 6, 7 and 10 contribute most to the binding. The observed destabilization of the complex upon removal of signal methyl groups from the hydrophobic side of the helix is comparable with the destabilization of proteins in which methyl groups have been removed from the inner core. We conclude that upon binding to p11 the hydrophobic side of the amphiphatic alpha-helix becomes fully buried.

Structure of an invertebrate gene encoding cytoplasmic intermediate filament (IF) proteins: implications for the origin and the diversification of IF proteins

The structure of the single gene encoding the cytoplasmic intermediate filament (IF) proteins in non-neuronal cells of the gastropod Helix aspersa is described. Genomic and cDNA sequences show that the gene is composed of 10 introns and 11 exons, spanning greater than 60 kb of DNA. Alternative RNA processing accounts for two mRNA families which encode two IF proteins differing only in their C-terminal sequence. The intron/exon organization of the Helix rod domain is identical to that of the vertebrate type III IF genes in spite of low overall protein sequence homology and the presence of an additional 42 residues in coil 1b of the invertebrate sequence. Intron position homology extends to the entire coding sequence comprising both the rod and tail domains when the invertebrate IF gene is compared with the nuclear lamin LIII gene of Xenopus laevis presented in the accompanying report of Döring and Stick. In contrast the intron patterns of the tail domains of the invertebrate IF and the lamin genes differ from those of the vertebrate type III genes. The combined data are in line with an evolutionary descent of cytoplasmic IF proteins from a nuclear lamin-like progenitor and suggest a mechanism for this derivation. The unique position of intron 7 in the Helix IF gene indicates that the archetype IF gene arose by the elimination of the nuclear localization sequence due to the recruitment of a novel splice site. The presumptive structural organization of the archetype IF gene allows predictions with respect to the later diversification of metazoan IF genes. Whereas models proposing a direct derivation of neurofilament genes seem unlikely, the earlier speculation of an mRNA transposition mechanism is compatible with current results.

Vimentin is preferentially expressed in high-grade ductal and medullary, but not in lobular breast carcinomas

Two hundred sixty-two invasive breast carcinomas dating from 1979 to 1984 were tested for vimentin and keratin on formaldehyde-fixed paraffin-embedded sections. None of 26 lobular carcinomas expressed vimentin. Vimentin expression in 10% or more of tumor cells was found in 78% of medullary (14 of 18), in 16% of ductal not otherwise specified (NOS) (35 of 214), and in two of four mucinous carcinomas. A further seven tumors showed vimentin expression in less than 1% to 10% of the cells. Vimentin was expressed in tumor cells of 30% (28 of 93) of grade III invasive ductal NOS carcinomas versus 7% (7 of 105) of grade II and 0% of grade I carcinomas (0 of 10). Vimentin was found to be preferentially expressed in tumors growing in broad, often anastomosing bands or sheets with extensive necrosis, scanty supportive stroma, high nuclear grade, and numerous mitoses. The authors conclude that vimentin is not detected in lobular carcinomas, but is preferentially expressed in medullary and in high-grade ductal NOS breast carcinomas.

Tailless keratins assemble into regular intermediate filaments in vitro

To study the influence of the non alpha-helical tail domain of keratins in filament formation, we prepared a truncated keratin 8 mutant, K8/tailless. Using site-directed in vitro mutagenesis we introduced a stop codon in the position coding for amino acid number 417 of the K8/wild-type sequence, thereby deleting 86 amino acids of the non alpha-helical tail domain but leaving the consensus sequence at the end of the rod domain intact. Expression of the truncated keratin 8 in Escherichia coli allowed us to purify the protein by a two-step procedure. The filament-forming capacity of the truncated K8 with wild-type K18 and K19 was analyzed using in vitro reconstitution. The in vitro assembly studies with K8/tailless and K18 wild-type indicate that the C-terminal tail domain of a type II keratin, including the homologous subdomain H2, is not required for filament formation. Moreover, reconstitution experiments with K8/tailless and K19, a naturally occurring tailless keratin I, show that the tail domains of type I as well as type II keratins are not an essential requirement for in vitro filament formation. Our results suggest that in vitro filament elongation does not depend on interactions between head and tail domains, although the tail domain might have a role in stabilization of intermediate filaments arising from certain keratin pairs.