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Biomedical subjects

Carlos Gonzalez

Publications and source records attributed to Carlos Gonzalez.

At least 19 recordsLinked to original sources
PubMed2007

Theoretical evidence for C-F bond activation by a fluoro-calix[4]pyrrole-tert-amine macrocycle.

Density functional theory as well as highly correlated ab initio molecular orbital theory was used to explore the possibility of activating C-F bonds in fluoroalkanes by organic macrocycles. The results indicate that the reaction between fluoro-calix [4]pyrrole-tert-amine and CH3F via a Menshutkin displacement mechanism is highly favorable and competitive from a thermochemical point of view with the very efficient C-Cl activation by a simple macrocyclic amine recently reported in the literature (Stanger, L. J.; Noll, B. C.; Gonzalez, C.; Marquez, M.; Smith, B. D. J. Am. Chem. Soc. 2005, 127, 4184).

Journal Article↗
PubMed2006

The molecular basis for T-type Ca2+ channel inhibition by G protein beta2gamma2 subunits.

Gbetagamma, a ubiquitous second messenger, relays external signals from G protein-coupled receptors to networks of intracellular effectors, including voltage-dependent calcium channels. Unlike high-voltage-activated Ca(2+) channels, the inhibition of low-voltage-activated Ca(2+) channels is subtype-dependent and mediated selectively by Gbeta(2)-containing dimers. Yet, the molecular basis for this exquisite selectivity remains unknown. Here, we used pure recombinant Gbetagamma subunits to establish that the Gbeta(2)gamma(2) dimer can selectively reconstitute the inhibition of alpha(1H) channels in isolated membrane patches. This inhibition is the result of a reduction in channel open probability that is not accompanied by a change in channel expression or an alteration in active-channel gating. By exchanging residues between the active Gbeta(2) subunit and the inactive Gbeta(1) subunit, we identified a cluster of amino acids that functionally distinguish Gbeta(2) from other Gbeta subunits. These amino acids on the beta-torus identify a region that is distinct from those regions that contact the Galpha subunit or other effectors.

Amino Acids↗
PubMed2006

Chemisorption-induced spin symmetry breaking in gold clusters and the onset of paramagnetism in capped gold nanoparticles.

We present a simple model to describe the induction of magnetic behavior on gold clusters upon chemisorption of one organic molecule with different chemical linkers. In particular, we address the problem of stability of the lowest lying singlet and show that for some linkers there exists a spin symmetry-breaking that lowers the energy and leads to preferential spin density localization on the gold atoms neighboring the chemisorption site. The model is basically an adaptation of the Stoner model for itinerant electron ferromagnetism to finite clusters and it may have important implications for our understanding of surface magnetism in larger nanosystems and its relevance to electronic transport in electrode-molecule interfaces.

Journal Article↗
PubMed2006

Exploring the use of conformationally locked aminoglycosides as a new strategy to overcome bacterial resistance.

The emergence of bacterial resistance to the major classes of antibiotics has become a serious problem over recent years. For aminoglycosides, the major biochemical mechanism for bacterial resistance is the enzymatic modification of the drug. Interestingly, in several cases, the oligosaccharide conformation recognized by the ribosomic RNA and the enzymes responsible for the antibiotic inactivation is remarkably different. This observation suggests a possible structure-based chemical strategy to overcome bacterial resistance; in principle, it should be possible to design a conformationally locked oligosaccharide that still retains antibiotic activity but that is not susceptible to enzymatic inactivation. To explore the scope and limitations of this strategy, we have synthesized several aminoglycoside derivatives locked in the ribosome-bound "bioactive" conformation. The effect of the structural preorganization on RNA binding, together with its influence on the aminoglycoside inactivation by several enzymes involved in bacterial resistance, has been studied. Our results indicate that the conformational constraint has a modest effect on their interaction with ribosomal RNA. In contrast, it may display a large impact on their enzymatic inactivation. Thus, the work presented herein provides a key example of how the conformational differences exhibited by these ligands within the binding pockets of the ribosome and of those enzymes involved in bacterial resistance can, in favorable cases, be exploited for designing new antibiotic derivatives with improved activity in resistant strains.

Acetyltransferases↗
PubMed2006

Surgical treatment of femoroacetabular impingement: evaluation of the effect of the size of the resection. Surgical technique.

BACKGROUND: In patients with symptomatic hip impingement, surgical resection of the femoral head-neck junction may improve the range of motion and relieve pain. A risk of this procedure is fracture. We evaluated the amount of resection of the anterolateral aspect of the femoral head-neck junction that can be done safely. METHODS: Cadaveric proximal femoral specimens (fifteen matched pairs) were divided into three groups: 10%, 30%, or 50% of the diameter of one femoral neck was removed, and the contralateral femoral neck was left intact to serve as the control. A compressive load was applied directly to the femoral head. Peak load, stiffness, and energy to fracture were compared among the groups. RESULTS: The energy to fracture differed significantly (p = 0.0015) among the 10%, 30%, and 50% resection groups. The peak load after the 50% resection was significantly less (p = 0.0025) than that after the 10% or 30% resection. With the numbers available, there was no significant difference in peak load between the 10% and 30% resections. CONCLUSIONS: Resection of up to 30% of the anterolateral quadrant of the head-neck junction did not significantly alter the load-bearing capacity of the proximal part of the femur. However, a 30% resection significantly decreased the amount of energy required to produce a fracture. Thirty percent should be considered to be the greatest feasible amount of resection because of the change in the pattern of the femoral head-neck response to axial loads that we observed.

Acetabulum↗
PubMed2005

Rapid fixation of methylene chloride by a macrocyclic amine.

A simple macrocyclic amine is alkylated by methylene chloride to give a quaternary ammonium chloride salt. When methylene chloride is the solvent, the reaction exhibits pseudo-first-order kinetics, and the reaction half-life at 25.0 degrees C is 2.0 min. The reaction half-life for a structurally related, acyclic amine is approximately 50 000 times longer. Detailed calculations favor a mechanism where the methylene chloride associates with the macrocycle to form an activated prereaction complex. The macrocyclic nitrogen subsequently attacks the methylene chloride with a classic SN2 trajectory, and although the carbon-chlorine bond breaks, the chloride leaving group does not separate from the newly formed cationic macrocycle, such that the product is a tightly associated ion-pair. X-ray crystal structures of the starting amine and the product salt, as well as kinetic data, support this mechanism.

Journal Article↗
PubMed2005

S3b amino acid residues do not shuttle across the bilayer in voltage-dependent Shaker K+ channels.

In voltage-dependent channels, positive charges contained within the S4 domain are the voltage-sensing elements. The "voltage-sensor paddle" gating mechanism proposed for the KvAP K+ channel has been the subject of intense discussion regarding its general applicability to the family of voltage-gated channels. In this model, the voltage sensor composed of the S3b and the S4 segment shuttles across the lipid bilayer during channel activation. Guided by this mechanism, we assessed here the accessibility of residues in the S3 segment of the Shaker K+ channel by using cysteine-scanning mutagenesis. Mutants expressed robust K+ currents in Xenopus oocytes and reacted with methanethiosulfonate ethyltrimethylammonium in both closed and open conformations of the channel. Because Shaker has a long S3-S4 linker segment, we generated a deletion mutant with only three residues to emulate the KvAP structure. In this short linker mutant, all of the tested residues in the S3b were accessible to methanethiosulfonate ethyltrimethylammonium in both closed and open conformations. Because the S3b moves together with the S4 domain in the paddle model, we tested the effects of deleting two negative charges or adding a positive charge to this region of the channel. We found that altering the S3b net charge does not modify the total gating charge involved in channel activation. We conclude that the S3b segment is always exposed to the external milieu of the Shaker K+ channel. Our results are incompatible with any model involving a large membrane displacement of segment S3b.

Amino Acid Sequence↗
PubMed2005

Structure of the functional domain of phi29 replication organizer: insights into oligomerization and dna binding.

The Bacillus subtilis phage phi29-encoded membrane protein p16.7 is one of the few proteins involved in prokaryotic membrane-associated DNA replication that has been characterized at a functional and biochemical level. In this work we have determined both the solution and crystal structures of its dimeric functional domain, p16.7C. Although the secondary structure of p16.7C is remarkably similar to that of the DNA binding homeodomain, present in proteins belonging to a large family of eukaryotic transcription factors, the tertiary structures of p16.7C and homeodomains are fundamentally different. In fact, p16.7C defines a novel dimeric six-helical fold. We also show that p16.7C can form multimers in solution and that this feature is a key factor for efficient DNA binding. Moreover, a combination of NMR and x-ray approaches, combined with functional analyses of mutants, revealed that multimerization of p16.7C dimers is mediated by a large protein surface that is characterized by a striking self-complementarity. Finally, the structural analyses of the p16.7C dimer and oligomers provide important clues about how protein multimerization and DNA binding are coupled.

Binding Sites↗
PubMed2005

Extended femoral osteotomy for revision of hip arthroplasty: results and complications.

Seventy-five revision total hip arthroplasties (73 patients) performed using an extended greater trochanteric osteotomy for exposure and an extensively porous-coated uncemented stem were reviewed after 2 years (range, 1 to 5). The mean osteotomy length was 14 cm (range, 7 to 19 cm) and fixation was with at least 2 cables. One stem was revised at 4 months for stem subsidence and loosening. Of the remaining 74 osteotomies, 73 healed without further procedures. A single nonunion was reoperated at 4 months and healed. Sixty-eight of 73 osteotomies healed with no migration and 5 did with less than 5 mm of proximal migration of the osteotomy fragment. Complications included 3 intraoperative and 1 postoperative osteotomy fragment fractures. Extended trochanteric osteotomy, executed preserving the fragment's vascularity and fixed with rigid fixation, can be performed with a low rate of complications.

Adult↗
PubMed2005

Surgical treatment of femoroacetabular impingement: evaluation of the effect of the size of the resection.

BACKGROUND: In patients with symptomatic hip impingement, surgical resection of the femoral head-neck junction may improve the range of motion and relieve pain. A risk of this procedure is fracture. We evaluated the amount of resection of the anterolateral aspect of the femoral head-neck junction that can be done safely. METHODS: Cadaveric proximal femoral specimens (fifteen matched pairs) were divided into three groups: 10%, 30%, or 50% of the diameter of one femoral neck was removed, and the contralateral femoral neck was left intact to serve as the control. A compressive load was applied directly to the femoral head. Peak load, stiffness, and energy to fracture were compared among the groups. RESULTS: The energy to fracture differed significantly (p = 0.0015) among the 10%, 30%, and 50% resection groups. The peak load after the 50% resection was significantly less (p = 0.0025) than that after the 10% or 30% resection. With the numbers available, there was no significant difference in peak load between the 10% and 30% resections. CONCLUSIONS: Resection of up to 30% of the anterolateral quadrant of the head-neck junction did not significantly alter the load-bearing capacity of the proximal part of the femur. However, a 30% resection significantly decreased the amount of energy required to produce a fracture. Thirty percent should be considered to be the greatest feasible amount of resection because of the change in the pattern of the femoral head-neck response to axial loads that we observed.

Aged↗
PubMed2004

Serum-free media for periosteal chondrogenesis in vitro.

Organ culture studies involving whole explants of periosteum have been useful for studying chondrogenesis, but to date the standard culture model for these explants has required the addition of fetal bovine serum to the media. Numerous investigators have succeeded in culturing chondrocytes and embryonic cells in serum-free conditions but there have been no studies focused on achieving a defined, serum-free media for culturing periosteal explants. The purpose of the present investigation was to determine if whole periosteal explants can be grown and produce cartilage in serum-free conditions, and to define the minimum media supplements that would be conducive to chondrogenesis. 321 periosteal explants were obtained from the medial proximal tibiae of 31 two month-old NZ white rabbits and cultured using a published agarose suspension organ culture model and DMEM for six weeks. The explants were cultured with and without fetal bovine serum or bovine serum albumin and exposed to transforming growth factor beta alone, a combination of growth factors we call ChondroMix (10 ng/ml transforming growth factor beta, 50 ng/ml basic fibroblast growth factor, and 5 microg/ml growth hormone), and/or ITS+ (2.08 microg/ml each of insulin, transferrin, and selenious acid, plus 1.78 microg/ml linoleic acid and 0.42 mg/ml BSA). Maximal chondrogenic stimulation in this study was observed with the combination of ChondroMix and ITS+. However, the minimal requirement to match or exceed the level of chondrogenic stimulation seen in the standard model (TGF-1 in 10% FBS) was achieved simply by the addition of 2.0 microg/ml insulin in 0.1% BSA-containing medium (p < 0.05). Therefore, based on our results, it would be reasonable to assume that insulin is the component in ITS+ responsible for the observed increase in total cartilage growth. Lower concentrations of insulin were not effective, suggesting that the observed effect of insulin requires activation of the IGF-1 receptor.

Animals↗
PubMed2004

Short-term psychological impact of predictive testing for Machado-Joseph disease: depression and anxiety levels in individuals at risk from the Azores (Portugal).

OBJECTIVE: The short-term impact of the pre-symptomatic genetic test (PT) for Machado-Joseph disease (MJD) in the Azores (Portuguese Islands) was assessed in 46 individuals at risk who completed the PT Program. METHODS: Scores for depression and anxiety were used as indicators of the subjects' emotional status immediately before the PT and 1 year after disclosure of the results. RESULTS: Global levels of participation in the Azorean PT Program for MJD were high (20.7%), particularly in Flores Island (35.8%). For the total sample, mean scores of depression and anxiety before and after the PT presented without clinical significance. No differences were found for depression and anxiety scores before and after the PT. Furthermore, when grouped by test results (carriers/non-carriers), there were no differences between pre- and post-test levels. CONCLUSIONS: Results indicate that the test result did not cause a decrease in the psychological well-being of the individuals tested. The high number of participants performing the PT in the small and isolated community of Flores Island, where MJD represents a source of stigma, was interpreted as an indication that in this particular population the PT offers the individuals at risk the possibility of liberating from a stigma, and, hence, from exclusion.

Adult↗
PubMed2003

Anion permeation in human ClC-4 channels.

ClC-4 and ClC-5 are mammalian ClC isoforms with unique ion conduction and gating properties. Macroscopic current recordings in heterologous expression systems revealed very small currents at negative potentials, whereas a substantially larger instantaneous current amplitude and a subsequent activation were observed upon depolarization. Neither the functional basis nor the physiological impact of these channel features are currently understood. Here, we used whole-cell recordings to study pore properties of human ClC-4 channels heterologously expressed in tsA201 or HEK293 cells. Variance analysis demonstrated that the prominent rectification of the instantaneous macroscopic current amplitude is due to a voltage-dependent unitary current conductance. The single channel amplitudes are very small, i.e., 0.10 +/- 0.02 pA at +140 mV for external Cl(-) and internal I(-). Conductivity and permeability sequences were determined for various external and internal anions, and both values increase for anions with lower dehydration energies. ClC-4 exhibits pore properties that are distinct from other ClC isoforms. These differences can be explained by assuming differences in the size of the pore narrowing and the electrostatic potentials within the ion conduction pathways.

Anions↗
PubMed2003

Molecular coupling between voltage sensor and pore opening in the Arabidopsis inward rectifier K+ channel KAT1.

Animal and plant voltage-gated ion channels share a common architecture. They are made up of four subunits and the positive charges on helical S4 segments of the protein in animal K+ channels are the main voltage-sensing elements. The KAT1 channel cloned from Arabidopsis thaliana, despite its structural similarity to animal outward rectifier K+ channels is, however, an inward rectifier. Here we detected KAT1-gating currents due to the existence of an intrinsic voltage sensor in this channel. The measured gating currents evoked in response to hyperpolarizing voltage steps consist of a very fast (tau = 318 +/- 34 micros at -180 mV) and a slower component (4.5 +/- 0.5 ms at -180 mV) representing charge moved when most channels are closed. The observed gating currents precede in time the ionic currents and they are measurable at voltages (less than or equal to -60) at which the channel open probability is negligible ( approximately 10-4). These two observations, together with the fact that there is a delay in the onset of the ionic currents, indicate that gating charge transits between several closed states before the KAT1 channel opens. To gain insight into the molecular mechanisms that give rise to the gating currents and lead to channel opening, we probed external accessibility of S4 domain residues to methanethiosulfonate-ethyltrimethylammonium (MTSET) in both closed and open cysteine-substituted KAT1 channels. The results demonstrate that the putative voltage-sensing charges of S4 move inward when the KAT1 channels open.

Algorithms↗
PubMed2003

A simple theoretical model to study the voltage dependence of the electronic structure of phenyl ethylene oligomers.

Although very few measurements have appeared in the open literature and there seems to be a controversy about the existence of the NDR phenomenon in molecules, the prospects of building such systems have attracted significant attention. In the work reported in this paper we used a model based on DFT calculations of the electronic structure of the 2'-amino-4,4'-di(ethynylphenyl)-5'-nitro-1-benzenethiolate molecule (previously reported to exhibit NDR behavior) in a capacitor-like electric field that mimics the potential spatial profile of the junction. Our results suggest that in these systems, there seems to be a correlation between a substantial charge density rearrangement of the neutral bridge at a threshold voltage and the NDR behavior observed in previous experiments. Our results highlight the importance of inclusion of the field in the study of electrified interfaces. We applied this model to a fluorine-substituted conjugated diethynylphenyl molecule and found that these calculations predict similar behavior. Results based on extended system calculations, including electrode-molecule interactions, confirm the validity of the model based on the isolated molecule and suggest the use of these simple models to rationally design molecular devices with similar switching characteristics.

Algorithms↗
PubMed2002

Psoriatic spondyloarthropathy: a comparative study between HLA-B27 positive and HLA-B27 negative disease.

OBJECTIVES: To evaluate the relative contribution of the human leukocyte antigen (HLA)-B27 to psoriatic spondyloarthropathy (PsSpA) susceptibility and to analyze whether this antigen contributes to disease expression. METHODS: This cross-sectional study included 70 patients (mean age 48 +/- 14.5 years; 44 men and 26 women). PsSpA was defined according to radiological findings (grade 2 or more sacroiliitis), and patients were classified into 3 main subtypes: isolated axial disease (n = 16), axial plus oligoarthritis (n = 29) and axial plus polyarthritis (n = 25). All patients were studied following a standard protocol that included the collection of demographic and epidemiological data, clinical history, radiographs, complementary tests, physical examination, and HLA-B27 testing (serological method). For functional evaluation, the Health Assessment Questionnaire-Specific for spondyloarthropathy (HAQ-S) was used. Patients with and without HLA-B27 antigen were compared on the basis of the data. RESULTS: Twenty-four patients (34%) carried the HLA-B27 antigen (RR 6.4, P <.0004). Fifty-six percent of those patients with the isolated axial pattern had this antigen, compared with 24% in the poly-arthritis axial pattern and 31% of those in the oligo-arthritis axial group (P =.016). Univariate analysis demonstrated correlations between HLA-B27 and an earlier age of onset for both psoriasis (P =.028) and arthritis (P =.006), male gender (P =.002), bilateral sacroiliitis (P =.002), and uveitis (P =.026). HLA-B27 negative patients developed more peripheral erosions than HLA-B27 positive patients (P =.05). No correlation was found between B27 and clinical symptoms of back involvement, syndesmophytes, or functional impairment. CONCLUSIONS: The HLA-B27 antigen is not only important for PsSpA susceptibility, but also determines some clinical features. This antigen was associated with earlier age of psoriasis and arthritis onset, bilateral sacroiliitis, and male gender. However, it was not associated with either the severity or extension of the spondylitic process or with functional impairment.

Arthritis, Psoriatic↗
PubMed2002

Counting channels: a tutorial guide on ion channel fluctuation analysis.

Ion channels open and close in a stochastic fashion, following the laws of probability. However, distinct from tossing a coin or a die, the probability of finding the channel closed or open is not a fixed number but can be modified (i.e., we can cheat) by some external stimulus, such as the voltage. Single-channel records can be obtained using the appropriate electrophysiological technique (e.g., patch clamp), and from these records the open probability and the channel conductance can be calculated. Gathering these parameters from a membrane containing many channels is not straightforward, as the macroscopic current I = iNP(o), where i is the single-channel current, N the number of channels, and P(o) the probability of finding the channel open, cannot be split into its individual components. In this tutorial, using the probabilistic nature of ion channels, we discuss in detail how i, N, and P(o max) (the maximum open probability) can be obtained using fluctuation (nonstationary noise) analysis (Sigworth FJ. G Gen Physiol 307: 97-129, 1980). We also analyze the sources of possible artifacts in the determination of i and N, such as channel rundown, inadequate filtering, and limited resolution of digital data acquisition by use of a simulation computer program (available at www.cecs.cl).

Animals↗