[Current aspects and new techniques in dislocation of the shoulder joint]. / Aktuelle Aspekte und neue Techniken bei Schultereckgelenksprengung.

With 12% of all injuries concerning the shoulder, acromioclavicular (AC) joint dislocations are a common injury especially in young and active patients. The Rockwood classification is widely accepted, which differentiates between six types depending on the degree of injury and the vertical dislocation. Because the classification does not adequately address the horizontal instability, its benefits are questionable and there is currently no consensus. For this reason, the classification and the therapy of these injuries are increasingly becoming the subject of scientific investigations. Whereas conservative treatment for type I and II injuries and operative treatment for type IV-VI injuries are widely accepted, there is still no agreement in treating type III lesions. The goal of this review article is to present the current evidence for the diagnostics, different classifications and therapeutic possibilities.

[Total ankle replacement for varus deformity]. / Sprunggelenkprothese bei Varusarthrose.

Coronal plane deformity has been found to be one of the main risk factors for poor clinical results, higher complication rates and failure of total ankle replacements. Initially, many authors considered a malalignment of more than 10° to be a contraindication for total ankle replacement, however, several publications later underlined the usefulness of the distinction of different etiologies of hindfoot malalignment. This subsequently led to suggestions for additional procedures in order to avoid early implant failure.The aim of the present article is to illustrate the different causes of varus malaligned arthritic ankles and to present procedures to balance these ankles at the time of replacement.

Subtalar and talonavicular arthrodesis through a single medial approach for the correction of severe planovalgus deformity.

We describe a retrospective review of the clinical and radiological parameters of 32 feet in 30 patients (10 men and 20 women) who underwent correction for malalignment of the hindfoot with a modified double arthrodesis through a medial approach. The mean follow-up was 21 months (13 to 37). Fusion was achieved in all feet at a mean of 13 weeks (6 to 30). Apart from the calcaneal pitch angle, all angular measurements improved significantly after surgery. Primary wound healing occurred without complications. The isolated medial approach to the subtalar and talonavicular joints allows good visualisation which facilitated the reduction and positioning of the joints. It was also associated with fewer problems with wound healing than the standard lateral approach.

Identification and functional characterization of the zeta-chain dimerization motif for TCR surface expression.

We recognized a common dimerization motif between the transmembrane (TM) domain of zeta-chain family members and glycophorin A. We have shown that a glycine within the zeta-dimerization motif is critical for zeta-homodimerization and also for its association with the TCR/CD3 complex. Similarly, two residues within the CD3 delta gamma TM domains have proven to be critical for their interaction with the zeta-homodimer. A three-dimensional homology model of the zeta-chain TM domain highlights potential residues preferentially involved either in the zeta 2-CD3 or zeta 2-TCR alpha beta association, confirming our experimental findings. These results indicate that, for symmetrical reasons, the zeta-homodimer participates in the TCR/CD3 complex assembly by interacting with CD3 gamma delta TM domains, thereby masking their degradation signals located in the cytoplasmic tails.

The extracellular domain of the zeta-chain is essential for TCR function.

The zeta-chain homodimer is a key component in the TCR complex and exerts its function through its cytoplasmic immunoreceptor-tyrosine activation motif (1). The zeta-chain extracellular (EC) domain is highly conserved; however, its functional and structural contributions to the TCR signaling have not been elucidated. We show that the EC domain of the zeta homodimer is essential for TCR surface expression. To gain a more detailed structural and functional information about the zeta-chain EC domain, we applied a cysteine scanning mutagenesis to conserved amino acids of the short domain. The results showed that the interchain disulfide bridge can be displaced by seven or eight amino acids along the EC domain. The TCR signaling efficacy was dramatically reduced during peptide/MHC engagement in the zeta mutants containing the displaced disulfide bond. These signaling defective zeta mutants produced an unconventional early tyrosine phosphorylation pattern. While the tyrosine phosphorylated forms of zeta (p21 and p23) could be observed during Ag stimulation, downstream signaling events such as the generation of phospho-p36, higher m.w. forms of phospho-zeta, and phospho-zeta/ZAP-70 complexes were impaired. Together these results suggest an important function of the phylogenetically conserved zeta-EC domain.

T cell receptor (TCR) antagonism without a negative signal: evidence from T cell hybridomas expressing two independent TCRs.

Antagonist peptides inhibit T cell responses by an unknown mechanism. By coexpressing two independent T cell receptors (TCRs) on a single T cell hybridoma, we addressed the question of whether antagonist ligands induce a dominant-negative signal that inhibits the function of a second, independent TCR. The two receptors, Valpha2Vbeta5 and Valpha2Vbeta10, restricted by H-2Kb and specific for the octameric peptides SIINFEKL and SSIEFARL, respectively, were coexpressed on the same cell. Agonist stimulation demonstrated that the two receptors behaved independently with regard to antigen-induced TCR downregulation and intracellular biochemical signaling. The exposure of one TCR (Valpha2Vbeta5) to antagonist peptides could not inhibit a second independent TCR (Valpha2Vbeta10) from responding to its antigen. Thus, our data clearly demonstrate that these antagonist ligands do not generate a dominant-negative signal which affects the responsiveness of the entire cell. In addition, a kinetic analysis showed that even 12 h after engagement with their cognate antigen and 10 h after reaching a steady-state of TCR internalization, T cells were fully inhibited by the addition of antagonist peptides. The window of susceptibility to antagonist ligands correlated exactly with the time required for the responding T cells to commit to interleukin 2 production. The data support a model where antagonist ligands can competitively inhibit antigenic peptides from productively engaging the TCR. This competitive inhibition is effective during the entire commitment period, where sustained TCR engagement is essential for full T cell activation.

The chicken TCR zeta-chain restores the function of a mouse T cell hybridoma.

The TCR/CD3 complex has been intensively studied in mammals, but it has been difficult to isolate homologues in other vertebrates. Here, we characterize the chicken zeta-chain, the first nonmammalian homologue identified. The comparison of mammalian and chicken zeta proteins revealed high identity of the transmembrane and the C-terminal cytoplasmic domains. Transfection of a mouse zeta-deficient cell line, with the chicken zeta gene, restored surface expression of the murine TCR/CD3 complex. The chicken zeta-chain was stably associated with the mouse TCR/CD3 components and fully restored its signaling capacity upon stimulation with Ab, superantigen, and peptide Ag. This is the first report of a nonmammalian TCR component that is capable of fully restoring a mammalian TCR in every aspect analyzed, thus demonstrating the enormous selective pressure to maintain the zeta-chain as a structural and signaling component over a period of 300 million years.

The short extracellular domain of the T cell receptor zeta chain is involved in assembly and signal transduction.

The zeta chain is required in the TCR complex to guarantee its surface expression and function. However, an understanding of the interaction(s) between the zeta chain and the other proteins in the TCR/CD3 has not yet been achieved. In this report, we attempt to assign a functional role to the short extracellular (EC) domain of the zeta chain by studying its unique positive charge, a lysine at position 9, because of its interesting location to the interchain disulphide bond of the zeta chain homodimer. We show that amino acid exchanges of lysine 9 to glycine, serine, cysteine or asparagine generate TCR complexes which are clearly defective in antigenic signalling. Interestingly, the non-conservative point mutations were segregating TCR complex signalling pathways. However, lysine 9 is not critical for TCR complex surface expression unless the positively charged lysine is exchanged for the negatively charged amino acid aspartic acid. The zeta chain mutant bearing a lysine to cysteine exchange is the sole mutant to be inefficiently co-precipitated with the TCR/CD3 complex suggesting a loose interaction of the zeta chain within the TCR complex.

Acidic receptor domains on both sides of the outer membrane mediate translocation of precursor proteins into yeast mitochondria.

Mitochondrial precursor proteins made in the cytosol bind to a hetero-oligomeric protein import receptor on the mitochondrial surface and then pass through the translocation channel across the outer membrane. This translocation step is accelerated by an acidic domain of the receptor subunit Mas22p, which protrudes into the intermembrane space. This 'trans' domain of Mas22p specifically binds functional mitochondrial targeting peptides with a Kd of < 1 microM and is required to anchor the N-terminal targeting sequence of a translocation-arrested precursor in the intermembrane space. If this Mas22p domain is deleted, respiration-driven growth of the cells is compromised and import of different precursors into isolated mitochondria is inhibited 3- to 8-fold. Binding of precursors to the mitochondrial surface appears to be mediated by cytosolically exposed acidic domains of the receptor subunits Mas20p and Mas22p. Translocation of a precursor across the outer membrane thus appears to involve sequential binding of the precursor's basic and amphiphilic targeting signal to acidic receptor domains on both sides of the membrane.

Dynamic interaction between Isp45 and mitochondrial hsp70 in the protein import system of the yeast mitochondrial inner membrane.

The protein import system of the yeast mitochondrial inner membrane includes at least three membrane proteins that presumably form a transmembrane channel as well as several chaperone proteins that mediate the import and refolding of precursor proteins. We show that one of the membrane proteins, Isp45, spans the mitochondrial inner membrane yet is extracted from this membrane at high pH. Solubilization of mitochondria with a nonionic detergent releases Isp45 as a complex with the chaperones mitochondrial hsp70 (mhsp70) and GrpEp. Both chaperones reversibly dissociate from Isp45 upon addition of ATP or adenosine 5'-[gamma-thio]triphosphate, suggesting that dissociation requires the binding of ATP. Control experiments indicate that the interaction between mhsp70 and Isp45 occurs in the intact mitochondria. We propose that Isp45 lines the inside of a proteinaceous channel across the inner membrane and that it is the membrane anchor for an ATP-driven "import motor" composed of mhsp70 and GrpEp. This arrangement is reminiscent of the protein transport systems of the yeast endoplasmic reticulum and the bacterial plasma membrane.

A mitochondrial homolog of bacterial GrpE interacts with mitochondrial hsp70 and is essential for viability.

Mitochondrial hsp70 (mhsp70) is located in the matrix and an essential component of the mitochondrial protein import system. To study the function of mhsp70 and to identify possible partner proteins we constructed a yeast strain in which all mhsp70 molecules carry a C-terminal hexa-histidine tag. The tagged mhsp70 appears to be functional in vivo. When an ATP depleted mitochondrial extract was incubated with a nickel-derivatized affinity resin, the resin bound not only mhsp70, but also a 23 kDa protein. This protein was dissociated from mhsp70 by ATP. ADP and GTP were much less effective in promoting dissociation whereas CTP and TTP were inactive. We cloned the gene encoding the 23 kDa protein. This gene, termed GRPE, encodes a 228 residue protein, whose sequence closely resembles that of the bacterial GrpE protein. Microsequencing the purified 23 kDa protein established it as the product of the yeast GRPE gene. Yeast GrpEp is made as a precursor that is cleaved upon import into isolated mitochondria. GrpEp is essential for viability. We suggest that this protein interacts with mhsp70 in a manner analogous to that of GrpE with DnaK of E.coli.

Protein import into yeast mitochondria: the inner membrane import site protein ISP45 is the MPI1 gene product.

Protein import across both mitochondrial membranes is mediated by the cooperation of two distinct protein transport systems, one in the outer and the other in the inner membrane. Previously we described a 45 kDa yeast mitochondrial inner membrane protein (ISP45) that can be cross-linked to a partially translocated precursor protein (Scherer et al., 1992). We have now purified ISP45 to homogeneity and identified it as the product of the nuclear MPI1 gene. Identity of ISP45 with the MPI1 gene product was shown by microsequencing of three tryptic ISP45 peptides and by demonstrating that an antibody against an Mpi1p-beta-galactosidase fusion protein specifically recognizes ISP45. Antibodies monospecific for ISP45 inhibited protein import into right-side-out mitochondrial inner membrane vesicles, but not into intact mitochondria. On solubilizing mitochondria, ISP45 was rapidly converted to a 40 kDa proteolytic fragment unless mitochondria were first denatured with trichloroacetic acid. The combined genetic and biochemical evidence identifies ISP45/Mpi1p as a component of the protein import system of the yeast mitochondrial inner membrane.