Structures of yeast ARF2 and ARL1: distinct roles for the N terminus in the structure and function of ARF family GTPases

Structures were determined by x-ray crystallography for two members of the ADP-ribosylation factor (ARF) family of regulatory GTPases, yeast ARF1 and ARL1, and were compared with previously determined structures of human ARF1 and ARF6. These analyses revealed an overall conserved fold but differences in primary sequence and length, particularly in an N-terminal loop, lead to differences in nucleotide and divalent metal binding. Packing of hydrophobic residues is central to the interplay between the N-terminal alpha-helix, switch I, and the interswitch region, which along with differences in surface electrostatics provide explanations for the different biophysical and biochemical properties of ARF and ARF-like proteins.

[Modification of particle replacement in a case of benign paroxysmal positional vertigo (BPPV) of the horizontal canal]

A variant of the particle repositioning maneuver was used in a patient diagnosed as benign paroxysmal positional vertigo of the horizontal canal. The patient was treated initially with Lempert's maneuver, but a paradoxical response was elicited by videonystagmography so we had to develop a maneuver adapted to the location of the patients otoliths. The likely physiopathology is discussed in the light of videonystagmographic events.

Structure of the human ADP-ribosylation factor 1 complexed with GDP

ADP-ribosylation factors (ARFs) are essential and ubiquitous in eukaryotes, being involved in vesicular transport and functioning as an activator of phospholipase D (refs 1, 2) and cholera toxin. The functions of ARF proteins in membrane traffic and organelle integrity are intimately tied to its reversible association with membranes and specific interactions with membrane phospholipids. One common feature of these functions is their regulation by the binding and hydrolysis of GTP. Here we report the three-dimensional structure of full-length human ARF1 (M(r) 21,000) in its GDP-bound non-myristoylated form. The presence of a unique amino-terminal alpha-helix and loop, together with differences in Mg2+ ligation and the existence of a non-crystallographic dimer, set this structure apart from other GTP-binding proteins. These features provide a structural basis for the GTP-dependent modulation of membrane affinity, the lack of intrinsic GTPase activity, and the nature of effector binding surfaces.

[Results of osteointegrated prosthesis of Audiant type]

Patient selection criteria, auditory results, complications, and patient satisfaction as related to implantation of an Audiant prosthesis in 1991-1992 are analyzed. We report our experience with this late-generation prosthesis in three patients compared with an earlier model implanted.

Time-dependent effects of estradiol and progesterone on the number of striatal dopaminergic D2-receptors

Recent evidence has shown that sexual steroids are able to modify the activity of the dopaminergic nigrostriatal pathway. Most of this evidence has been obtained from the individual effects of these hormones, but there is less information about possible interrelationships between both. In order to further explore this question, ovariectomized adult rats were submitted to estradiol (E2) or vehicle injections during 3 days and, at the third day, were also submitted to a single injection of progesterone (P) or vehicle at 4, 10, 24 and 32 h before decapitation. Additionally, the effect of injections of 2-hydroxyestradiol (2OH-E2), which has been involved as local mediator in the effects of E2, was also examined. The two striata of each animal were removed and used for determination of number and affinity of dopamine D2-receptors, using [3H]spiroperidol as ligand. Administration of E2 produced a significant reduction in the number of striatal dopaminergic receptors 10 h after the last steroid injection, which was followed by an increase at 24 h. Administration of P briefly decreased the number of dopaminergic receptors at 4 h after the steroid injection. This effect was not observed in animals pretreated with E2, in which administration of P produced an apparent increase 24 h after the steroid treatment. On the other hand, the 2-hydroxylated derivative of E2 does not seem to mediate in the stimulatory action of this estrogen, since it was unable to increase the number of dopaminergic receptors by itself or priming the action of P. The affinity of dopaminergic receptors for [3H]spiroperidol was not significantly altered after all the steroid treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

Reversed-phase high-performance liquid chromatography of protected peptide segments

There is little evidence that reversed-phase high-performance liquid chromatography can be successfully used in the analysis of protected peptide segments. The use of C18 and CN packings and mobile phases containing water-acetonitrile with or without propionic acid in the separation of complex mixtures of synthetic protected peptides is reported. CN packings show a lower efficiency and exhibit poorer resolution than C18 packings but provide different separations. The addition of propionic acid to the mobile phase increases the retention time of peptides but also provides dramatic and useful changes in selectivity. Retention is not related to the molecular mass of the protected peptides but mainly to their hydrophobicity.