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Gamez J, Navarro C, Andreu AL, Fernandez JM, Palenzuela L, Tejeira S, Fernandez-Hojas R, Schwartz S, Karadimas C, DiMauro S, Hirano M, Cervera C. Autosomal dominant limb-girdle muscular dystrophy: a large kindred with evidence for anticipation. Neurology 2001; 56:450-4. [PMID: 11222786 DOI: 10.1212/wnl.56.4.450] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
BACKGROUND Fourteen genetically distinct forms of limb-girdle muscular dystrophy (LGMD) have been identified, including five types of autosomal dominant LGMD (AD-LGMD). OBJECTIVE To describe clinical, histologic, and genetic features of a large Spanish kindred with LGMD and apparent autosomal dominant inheritance spanning five generations. METHOD The authors examined 61 members of the family; muscle biopsies were performed on five patients. Linkage analysis assessed chromosomal loci associated with other forms of AD-LGMD. RESULTS A total of 32 individuals had weakness of the pelvic and shoulder girdles. Severity appeared to worsen in successive generations. Muscle biopsy findings were nonspecific and compatible with MD. Linkage analysis to chromosomes 5q31, 1q11-q21, 3p25, 6q23, and 7q demonstrated that this disease is not allelic to LGMD forms 1A, 1B, 1C, 1D, and 1E. CONCLUSIONS This family has a genetically distinct form of AD-LGMD. The authors are currently performing a genome-wide scan to identify the disease locus.
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Oberhauser AF, Hansma PK, Carrion-Vazquez M, Fernandez JM. Stepwise unfolding of titin under force-clamp atomic force microscopy. Proc Natl Acad Sci U S A 2001; 98:468-72. [PMID: 11149943 PMCID: PMC14610 DOI: 10.1073/pnas.98.2.468] [Citation(s) in RCA: 209] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Here we demonstrate the implementation of a single-molecule force clamp adapted for use with an atomic force microscope. We show that under force-clamp conditions, an engineered titin protein elongates in steps because of the unfolding of its modules and that the waiting times to unfold are exponentially distributed. Force-clamp measurements directly measure the force dependence of the unfolding probability and readily captures the different mechanical stability of the I27 and I28 modules of human cardiac titin. Force-clamp spectroscopy promises to be a direct way to probe the mechanical stability of elastic proteins such as those found in muscle, the extracellular matrix, and cell adhesion.
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Vano E, Gonzalez L, Ten JI, Fernandez JM, Guibelalde E, Macaya C. Skin dose and dose-area product values for interventional cardiology procedures. Br J Radiol 2001; 74:48-55. [PMID: 11227777 DOI: 10.1259/bjr.74.877.740048] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
Coronary angiography and percutaneous transluminal coronary angioplasty procedures performed in four different facilities were monitored in the present study by measuring maximum skin dose, dose-area product and other operational parameters. Radiographic slow film, thermoluminescent dosemeters and transmission ion chambers were used to measure dose related quantities. Values of 107-711 mGy for maximum skin dose and 27.3-370.6 Gy cm2 for dose-area product were found, together with cumulative skin dose estimates of 110-3706 mGy. A discussion of the relationship of measured dose-area product and skin dose values is made using a field concentration factor defined as a way to interpret the findings. No general correlation was observed between dose-area product and maximum skin dose. Cumulative skin dose estimates throughout a procedure should be discarded as a realistic method for assessing deterministic risk in cardiology procedures. Slow film in addition to thermoluminescent dosemeters for measurement of maximum skin dose is a good alternative, especially for complex interventional procedures. For repeated procedures, combining film and dose-area product monitoring favours optimization of radiation protection for the patient.
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Li H, Carrion-Vazquez M, Oberhauser AF, Marszalek PE, Fernandez JM. Point mutations alter the mechanical stability of immunoglobulin modules. NATURE STRUCTURAL BIOLOGY 2000; 7:1117-20. [PMID: 11101892 DOI: 10.1038/81964] [Citation(s) in RCA: 189] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Immunoglobulin-like modules are common components of proteins that play mechanical roles in cells such as muscle elasticity and cell adhesion. Mutations in these proteins may affect their mechanical stability and thus may compromise their function. Using single molecule atomic force microscopy (AFM) and protein engineering, we demonstrate that point mutations in two beta-strands of an immunoglobulin module in human cardiac titin alter the mechanical stability of the protein, resulting in mechanical phenotypes. Our results demonstrate a previously unrecognized class of phenotypes that may be common in cell adhesion and muscle proteins.
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Calvo F, Teijeira S, Fernandez JM, Teijeiro A, Fernandez-Hojas R, Fernandez-Lopez XA, Martin E, Navarro C. Evaluation of heart involvement in gamma-sarcoglycanopathy (LGMD2C). A study of ten patients. Neuromuscul Disord 2000; 10:560-6. [PMID: 11053682 DOI: 10.1016/s0960-8966(00)00147-4] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Thorough non-invasive cardiovascular studies were conducted in a series of ten gamma-sarcoglycanopathy Gypsy patients with the founder C283Y mutation in 13q12. Results were compared with those obtained in an age-matched group of normal boys and girls. The studies included electrocardiographic and echocardiographic evaluations using pulsed wave Doppler tissue imaging to assess regional diastolic function and myocardial velocities at various levels. This study confirms the significant electrocardiographic abnormalities described in previous studies. Furthermore, measurement of myocardial velocity at different levels demonstrated an abnormal relaxation pattern in the tricuspid annulus in four of the oldest patients, which strongly suggests intrinsic myocardial involvement of the right ventricle. To our knowledge, these specific studies have not been previously performed in a clinically and genetically homogeneous group of gamma-sarcoglycanopathy patients and suggest primary myocardial involvement probably due to gamma-sarcoglycan deficiency in cardiac muscle fibres. Our results could be of interest in the follow-up of these patients and the prevention and treatment of late cardiological complications.
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Bunting LD, Tarifa TA, Crochet BT, Fernandez JM, Depew CL, Lovejoy JC. Effects of dietary inclusion of chromium propionate and calcium propionate on glucose disposal and gastrointestinal development in dairy calves. J Dairy Sci 2000; 83:2491-8. [PMID: 11104268 DOI: 10.3168/jds.s0022-0302(00)75141-1] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
In experiment 1, 21 male Holstein calves (43.9 kg) were fed only milk replacer at 1.4% of their body weight as dry matter for 6 wk. Dietary treatments included a commercial milk replacer (22% protein, 15% fat) containing (dry basis) either 6.4% Ca propionate or 6.4% dextrose (control) and either 0 or 0.5 mg/kg of supplemental Cr as Cr propionate. Neither Cr nor Ca propionate affected body weight gain; however, Ca propionate tended to increase the growth of the entire foregut measured after slaughter at 6 wk of age. A Minimal Model glucose tolerance test indicated that insulin sensitivity was not affected by treatment. However, calves fed Cr had higher glucose disappearance indexes than controls when propionate was not fed (0.013 vs. 0.019 units) but similar clearance when propionate was included (0.018 vs. 0.018 units, Cr x P interaction). The area under the glucose response curves after propionate-loading tests was much greater for calves fed the Cr versus control replacer when propionate was not present; however, when propionate was included, the response was less dramatic. In experiment 2, 25 Holstein calves were used to study performance and metabolic responses when milk replacer, and then postweaning starter, were supplemented with 0.5 mg/kg of Cr as Cr propionate. The metabolic responses of these calves were not affected by treatment. Overall, combined data suggested that supplemental Cr may improve glucose effectiveness; however, these responses seemed to be attenuated by supplemental propionate.
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132
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Ramos A, Mate B, Tejeda G, Fernandez JM, Montero S. Raman spectroscopy of hypersonic shock waves. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 2000; 62:4940-4945. [PMID: 11089040 DOI: 10.1103/physreve.62.4940] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2000] [Revised: 05/25/2000] [Indexed: 05/23/2023]
Abstract
Raman spectroscopy is shown to be an efficient diagnostic methodology for the study of hypersonic shock waves. As a test, absolute density and rotational population profiles have been measured across five representative normal shock waves of N2 generated in a free jet, spanning the Mach number range 7.7<M<15.3. The interconversion of three differentiated populations (cold, scattered, and rethermalized molecules) across these shock waves shows a largely bimodal rotational distribution function with additional contribution of scattered molecules, in close analogy with the velocity distribution function known from helium shock waves [G. Pham-Van-Diep et al., Science 245, 624 (1989)]. Quantitative data on invariance trends of density profiles and properties of the wake beyond the shock waves are reported.
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133
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Fisher TE, Carrion-Vazquez M, Fernandez JM. Intracellular Ca(2+) channel immunoreactivity in neuroendocrine axon terminals. FEBS Lett 2000; 482:131-8. [PMID: 11018536 DOI: 10.1016/s0014-5793(00)02043-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The concentration of neuroendocrine terminals in the neurohypophysis facilitates the identification and localization of Ca(2+) channel subtypes near neuroendocrine release sites. Immunoblots of rat neurohypophysial tissue identified the alpha(1)1.3, alpha(1)2.1, alpha(1)2.2, and alpha(1)2.3 Ca(2+) channel subunits. Immunofluorescence staining of axon terminal plasma membranes was weak, suggesting that Ca(2+) channels are dispersed. This contrasts with the highly punctate alpha(1)2.2 immunoreactivity in bovine chromaffin cells; the neurohypophysial terminals may therefore lack the specialized release zones found in those cells. Immunofluorescence and immunogold labeling identify dense core granule-like structures in the terminal cytoplasm containing multiple Ca(2+) channel types. Ca(2+) channels in internal membranes may play an important role in channel targeting and distribution in neuroendocrine cells.
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134
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Fisher TE, Carrion-Vazquez M, Oberhauser AF, Li H, Marszalek PE, Fernandez JM. Single molecular force spectroscopy of modular proteins in the nervous system. Neuron 2000; 27:435-46. [PMID: 11055427 DOI: 10.1016/s0896-6273(00)00055-6] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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135
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Fisher TE, Marszalek PE, Fernandez JM. Stretching single molecules into novel conformations using the atomic force microscope. NATURE STRUCTURAL BIOLOGY 2000; 7:719-24. [PMID: 10966637 DOI: 10.1038/78936] [Citation(s) in RCA: 255] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
A dense network of interconnected proteins and carbohydrates forms the complex mechanical scaffold of living tissues. The recently developed technique of single molecule force spectroscopy using the atomic force microscope (AFM) has enabled a detailed analysis of the force-induced conformations of these molecules and the determinants of their mechanical stability. These studies provide some of the basic knowledge required to understand the mechanical interactions that define all biological organisms.
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136
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Marszalek PE, Greenleaf WJ, Li H, Oberhauser AF, Fernandez JM. Atomic force microscopy captures quantized plastic deformation in gold nanowires. Proc Natl Acad Sci U S A 2000; 97:6282-6. [PMID: 10841533 PMCID: PMC18594 DOI: 10.1073/pnas.97.12.6282] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Scanning probe microscopy has become a powerful tool to detect structural changes in small clusters of atoms. Herein, we use an atomic force microscope to measure the length of gold nanowire structures during extension and compression cycles. We have found that nanowires elongate under force in quantized steps of up to three integer multiples of 1.76 A and that they shorten spontaneously in steps of 1.52 A. Our results can be explained by the sliding of crystal planes within the gold nanowires creating stacking faults that change the local structure from face-centered cubic to hexagonal close packed. Our data also show that there can be up to three simultaneous slip events, in good agreement with the tetrahedral arrangement of slip planes in a gold crystal. These experiments provide direct evidence for the mechanism underlying the plastic deformation of a nanowire. A similar approach can be used to examine the atomic events underlying the plastic failure of other metals and their alloys.
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Li H, Oberhauser AF, Fowler SB, Clarke J, Fernandez JM. Atomic force microscopy reveals the mechanical design of a modular protein. Proc Natl Acad Sci U S A 2000; 97:6527-31. [PMID: 10823913 PMCID: PMC18646 DOI: 10.1073/pnas.120048697] [Citation(s) in RCA: 242] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Tandem modular proteins underlie the elasticity of natural adhesives, cell adhesion proteins, and muscle proteins. The fundamental unit of elastic proteins is their individually folded modules. Here, we use protein engineering to construct multimodular proteins composed of Ig modules of different mechanical strength. We examine the mechanical properties of the resulting tandem modular proteins by using single protein atomic force microscopy. We show that by combining modules of known mechanical strength, we can generate proteins with novel elastic properties. Our experiments reveal the simple mechanical design of modular proteins and open the way for the engineering of elastic proteins with defined mechanical properties, which can be used in tissue and fiber engineering.
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138
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O'Neill of Tyrone A, Fernandez JM. Dissociative disorder associated with a colloid cyst of the third ventricle: organic or psychogenic amnesia? PSYCHOTHERAPY AND PSYCHOSOMATICS 2000; 69:108-9. [PMID: 10671832 DOI: 10.1159/000012374] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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139
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Carrion-Vazquez M, Oberhauser AF, Fisher TE, Marszalek PE, Li H, Fernandez JM. Mechanical design of proteins studied by single-molecule force spectroscopy and protein engineering. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2000. [PMID: 11106807 DOI: 10.1016/b978-008044031-6/50032-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Mechanical unfolding and refolding may regulate the molecular elasticity of modular proteins with mechanical functions. The development of the atomic force microscopy (AFM) has recently enabled the dynamic measurement of these processes at the single-molecule level. Protein engineering techniques allow the construction of homomeric polyproteins for the precise analysis of the mechanical unfolding of single domains. alpha-Helical domains are mechanically compliant, whereas beta-sandwich domains, particularly those that resist unfolding with backbone hydrogen bonds between strands perpendicular to the applied force, are more stable and appear frequently in proteins subject to mechanical forces. The mechanical stability of a domain seems to be determined by its hydrogen bonding pattern and is correlated with its kinetic stability rather than its thermodynamic stability. Force spectroscopy using AFM promises to elucidate the dynamic mechanical properties of a wide variety of proteins at the single molecule level and provide an important complement to other structural and dynamic techniques (e.g., X-ray crystallography, NMR spectroscopy, patch-clamp).
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McCormick ME, French DD, Brown TF, Cuomo GJ, Chapa AM, Fernandez JM, Beatty JF, Blouin DC. Crude protein and rumen undergradable protein effects on reproduction and lactation performance of Holstein cows. J Dairy Sci 1999; 82:2697-708. [PMID: 10629817 DOI: 10.3168/jds.s0022-0302(99)75526-8] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
We conducted a study to determine the effects of excess dietary crude protein (CP) and rumen undegradable protein (RUP) on reproduction and lactation performance of Holstein cows. During each of three yearly replicates, cows were blocked by previous mature equivalent milk production and randomly assigned at calving (n = 47; partum group) or at 42 +/- 21 d postpartum (n = 134; postpartum group) to the following dietary treatments: 1) ryegrass pasture supplemented with a corn and soybean meal grain mix (high CP, moderate RUP); 2) ryegrass pasture mornings and corn silage evenings, supplemented with grain as in diet 1 (moderate CP, moderate RUP control diet), and 3) ryegrass pasture mornings and corn silage evenings, supplemented with a grain mix containing corn, soybean meal, corn gluten meal, and blood meal (moderate CP, high RUP). Dietary CP and RUP concentrations were approximately 23.1, 5.8; 17.7, 5.0; and 17.2, 6.8% of dry matter for diets 1 to 3, respectively. Plasma urea N concentrations were highest in cows fed diet 1 (25.0 mg/dl), intermediate in cows on diet 2 (20.1 mg/dl), and lowest in cows on diet 3 (18.5 mg/dl). Cows fed excess dietary protein (diet 1) exhibited lower first breeding pregnancy rates (24.1 vs. 41.0%) and lower overall pregnancy rates (53.4 vs. 75.4%) than did cows fed diet 2, increasing time nonpregnant by an average of 15.1 d per cow. Reproductive performance was similar between cows fed diets 2 and 3. Mean fat-corrected milk (FCM) yield was not affected by protein concentration (diet 1 vs. 2); however, partum group cows that received supplemental RUP (diet 3) produced more 3.5% FCM than controls in early lactation. Feeding grain diets that contained excess dietary protein impaired the reproductive performance of dairy cows grazing ryegrass.
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141
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Marszalek PE, Lu H, Li H, Carrion-Vazquez M, Oberhauser AF, Schulten K, Fernandez JM. Mechanical unfolding intermediates in titin modules. Nature 1999; 402:100-3. [PMID: 10573426 DOI: 10.1038/47083] [Citation(s) in RCA: 701] [Impact Index Per Article: 28.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The modular protein titin, which is responsible for the passive elasticity of muscle, is subjected to stretching forces. Previous work on the experimental elongation of single titin molecules has suggested that force causes consecutive unfolding of each domain in an all-or-none fashion. To avoid problems associated with the heterogeneity of the modular, naturally occurring titin, we engineered single proteins to have multiple copies of single immunoglobulin domains of human cardiac titin. Here we report the elongation of these molecules using the atomic force microscope. We find an abrupt extension of each domain by approximately 7 A before the first unfolding event. This fast initial extension before a full unfolding event produces a reversible 'unfolding intermediate' Steered molecular dynamics simulations show that the rupture of a pair of hydrogen bonds near the amino terminus of the protein domain causes an extension of about 6 A, which is in good agreement with our observations. Disruption of these hydrogen bonds by site-directed mutagenesis eliminates the unfolding intermediate. The unfolding intermediate extends titin domains by approximately 15% of their slack length, and is therefore likely to be an important previously unrecognized component of titin elasticity.
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West JW, Hill GM, Fernandez JM, Mandebvu P, Mullinix BG. Effects of dietary fiber on intake, milk yield, and digestion by lactating dairy cows during cool or hot, humid weather. J Dairy Sci 1999; 82:2455-65. [PMID: 10575613 DOI: 10.3168/jds.s0022-0302(99)75497-4] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Lactating cows were offered diets with increasing neutral detergent fiber concentrations to determine the effects on intake, milk yield and composition, blood hormones, and nutrient digestion during cool or hot weather conditions. Tifton 85 bermudagrass hay was substituted for corn silage so that the forage portion of diets were: 1) 40% corn silage (control), 2) 32.4% corn silage, 7.6% bermudagrass, 3) 24.8% corn silage, 15.2% bermudagrass, or 4) 17.2% corn silage, 22.8% bermudagrass (dry basis). Dietary neutral detergent fiber concentrations (% dry matter) were 30.2, 33.8, 37.7, and 42.0, respectively. Intake of dry matter declined with increasing dietary neutral detergent fiber during cool and hot periods, but intake adjusted for cool weather treatment differences did not change further during hot weather. Milk yield declined linearly with increasing neutral detergent fiber during cool weather and changed quadratically during hot weather. Milk temperature declined with increasing dietary neutral detergent fiber for the p.m. milking during the cool period and declined with increasing dietary neutral detergent fiber for the a.m. and p.m. milkings during the hot period. Digestibility of neutral detergent fiber improved and ruminal turnover of particulate digesta was increased with greater dietary neutral detergent fiber content. No dietary fiber level by hot weather interaction was observed, suggesting that total energy intake may have and a greater effect on milk yield than dietary fiber content during hot, humid weather.
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143
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Oberhauser AF, Marszalek PE, Carrion-Vazquez M, Fernandez JM. Single protein misfolding events captured by atomic force microscopy. NATURE STRUCTURAL BIOLOGY 1999; 6:1025-8. [PMID: 10542093 DOI: 10.1038/14907] [Citation(s) in RCA: 168] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Using single protein atomic force microscopy (AFM) techniques we demonstrate that after repeated mechanical extension/relaxation cycles, tandem modular proteins can misfold into a structure formed by two neighboring modules. The misfolding is fully reversible and alters the mechanical topology of the modules while it is about as stable as the original fold. Our results show that modular proteins can assume a novel misfolded state and demonstrate that AFM is able to capture, in real time, rare misfolding events at the level of a single protein.
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Fisher TE, Marszalek PE, Oberhauser AF, Carrion-Vazquez M, Fernandez JM. The micro-mechanics of single molecules studied with atomic force microscopy. J Physiol 1999; 520 Pt 1:5-14. [PMID: 10517795 PMCID: PMC2269551 DOI: 10.1111/j.1469-7793.1999.00005.x] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
The atomic force microscope (AFM) in its force-measuring mode is capable of effecting displacements on an angstrom scale (10 A = 1 nm) and measuring forces of a few piconewtons. Recent experiments have applied AFM techniques to study the mechanical properties of single biological polymers. These properties contribute to the function of many proteins exposed to mechanical strain, including components of the extracellular matrix (ECM). The force-bearing proteins of the ECM typically contain multiple tandem repeats of independently folded domains, a common feature of proteins with structural and mechanical roles. Polysaccharide moieties of adhesion glycoproteins such as the selectins are also subject to strain. Force-induced extension of both types of molecules with the AFM results in conformational changes that could contribute to their mechanical function. The force-extension curve for amylose exhibits a transition in elasticity caused by the conversion of its glucopyranose rings from the chair to the boat conformation. Extension of multi-domain proteins causes sequential unraveling of domains, resulting in a force-extension curve displaying a saw tooth pattern of peaks. The engineering of multimeric proteins consisting of repeats of identical domains has allowed detailed analysis of the mechanical properties of single protein domains. Repetitive extension and relaxation has enabled direct measurement of rates of domain unfolding and refolding. The combination of site-directed mutagenesis with AFM can be used to elucidate the amino acid sequences that determine mechanical stability. The AFM thus offers a novel way to explore the mechanical functions of proteins and will be a useful tool for studying the micro-mechanics of exocytosis.
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145
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Fisher TE, Oberhauser AF, Carrion-Vazquez M, Marszalek PE, Fernandez JM. The study of protein mechanics with the atomic force microscope. Trends Biochem Sci 1999; 24:379-84. [PMID: 10500301 DOI: 10.1016/s0968-0004(99)01453-x] [Citation(s) in RCA: 208] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The unfolding and folding of single protein molecules can be studied with an atomic force microscope (AFM). Many proteins with mechanical functions contain multiple, individually folded domains with similar structures. Protein engineering techniques have enabled the construction and expression of recombinant proteins that contain multiple copies of identical domains. Thus, the AFM in combination with protein engineering has enabled the kinetic analysis of the force-induced unfolding and refolding of individual domains as well as the study of the determinants of mechanical stability.
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146
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Carrion-Vazquez M, Marszalek PE, Oberhauser AF, Fernandez JM. Atomic force microscopy captures length phenotypes in single proteins. Proc Natl Acad Sci U S A 1999; 96:11288-92. [PMID: 10500169 PMCID: PMC18026 DOI: 10.1073/pnas.96.20.11288] [Citation(s) in RCA: 170] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We use single-protein atomic force microscopy techniques to detect length phenotypes in an Ig module. To gain amino acid resolution, we amplify the mechanical features of a single module by engineering polyproteins composed of up to 12 identical repeats. We show that on mechanical unfolding, mutant polyproteins containing five extra glycine residues added to the folded core of the module extend 20 A per module farther than the wild-type polyproteins. By contrast, similar insertions near the N or C termini have no effect. Hence, our atomic force microscopy measurements readily discriminate the location of the insert and measure its size with a resolution similar to that of NMR and x-ray crystallography.
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147
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Fisher TE, Fernandez JM. Pulsed laser imaging of Ca(2+) influx in a neuroendocrine terminal. J Neurosci 1999; 19:7450-7. [PMID: 10460251 PMCID: PMC6782522] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/13/2023] Open
Abstract
The surge of Ca(2+) that triggers vesicle fusion is shaped by the distribution of Ca(2+) channels and the physical relationship between those channels and the exocytotic apparatus. Although channels and the release apparatus are thought to be tightly associated at fast synapses, the arrangement at neuroendocrine cells is less clear. The distribution of Ca(2+) influx near release sites is difficult to determine because of spatial and temporal limitations on Ca(2+) imaging techniques. We now present spatially resolved images of Ca(2+) influx into rat neuroendocrine terminals on a millisecond time scale. Images of voltage-dependent Ca(2+) influx into neurohypophysial terminals were captured after excitation of Ca(2+)-sensitive dyes with pulses of laser light lasting a fraction of a microsecond. Submembranous Ca(2+) increases were detected during the first millisecond of an evoked Ca(2+) tail current. Steep gradients of Ca(2+) were evident, with concentrations near the membrane reaching above 1 microM during a 30 msec depolarization. Ca(2+) influx appeared evenly distributed, even when diffusion was restricted with an exogenous Ca(2+) chelator. During longer depolarizations, mean and peak Ca(2+) concentrations reached an asymptote in parallel, suggesting that Ca(2+) binding proteins near the membrane rapidly buffer Ca(2+) and do not become saturated during prolonged influx. These data support the hypothesis that exocytosis is activated in these terminals by the summation of influx through multiple, randomly spaced Ca(2+) channels.
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148
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Marszalek PE, Pang YP, Li H, El Yazal J, Oberhauser AF, Fernandez JM. Atomic levers control pyranose ring conformations. Proc Natl Acad Sci U S A 1999; 96:7894-8. [PMID: 10393918 PMCID: PMC22158 DOI: 10.1073/pnas.96.14.7894] [Citation(s) in RCA: 120] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Atomic force microscope manipulations of single polysaccharide molecules have recently expanded conformational chemistry to include force-driven transitions between the chair and boat conformers of the pyranose ring structure. We now expand these observations to include chair inversion, a common phenomenon in the conformational chemistry of six-membered ring molecules. We demonstrate that by stretching single pectin molecules (1 --> 4-linked alpha-D-galactouronic acid polymer), we could change the pyranose ring conformation from a chair to a boat and then to an inverted chair in a clearly resolved two-step conversion: 4C1 right arrow over left arrow boat right arrow over left arrow 1C4. The two-step extension of the distance between the glycosidic oxygen atoms O1 and O4 determined by atomic force microscope manipulations is corroborated by ab initio calculations of the increase in length of the residue vector O1O4 on chair inversion. We postulate that this conformational change results from the torque generated by the glycosidic bonds when a force is applied to the pectin molecule. Hence, the glycosidic bonds act as mechanical levers, driving the conformational transitions of the pyranose ring. When the glycosidic bonds are equatorial (e), the torque is zero, causing no conformational change. However, when the glycosidic bond is axial (a), torque is generated, causing a rotation around C---C bonds and a conformational change. This hypothesis readily predicts the number of transitions observed in pyranose monomers with 1a-4a linkages (two), 1a-4e (one), and 1e-4e (none). Our results demonstrate single-molecule mechanochemistry with the capability of resolving complex conformational transitions.
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Gentry LR, Fernandez JM, Ward TL, White TW, Southern LL, Bidner TD, Thompson DL, Horohov DW, Chapa AM, Sahlu T. Dietary protein and chromium tripicolinate in Suffolk wether lambs: effects on production characteristics, metabolic and hormonal responses, and immune status. J Anim Sci 1999; 77:1284-94. [PMID: 10340598 DOI: 10.2527/1999.7751284x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Thirty-two Suffolk wether lambs were fed for 84 d in a 2 x 2 factorial experiment using two levels of dietary protein (9.0 to 12.1% CP, low protein, LP; or 12.8 to 14.4% CP, high protein, HP) and supplemental Cr (none, C; or 400 ppb Cr as chromium tripicolinate, Cr). At 14- to 21-d intervals, lambs were weighed, and jugular blood samples were collected. Mean ADG and carcass weight (P > .10) did not differ. In lambs fed HP, Cr reduced liver weight and increased kidney weight (P < .01). Lambs fed HP had elevated plasma urea N (PUN; P < .01) and albumin (P < .04). During an i.v. epinephrine challenge on d 43, plasma cortisol declined in lambs fed Cr (Cr x time, P < .03) and in lambs fed LP (CP x time, P < .001). An i.v. glucose tolerance test conducted 3 h later showed that supplemental Cr decreased glucose clearance rate in lambs fed HP (CP x Cr, P < .10) but not in lambs fed LP. On d 62, PUN was increased in lambs fed HP (P < .001) between 0 and 3 h postprandial, and there was a Cr x CP interaction (P < .04). Postprandial plasma NEFA declined with Cr vs C (Cr x time, P < .07) and with HP vs LP (CP x time, P < .10). By d 66, lambs fed Cr had an elevated (P < .03) blood platelet and fibrinogen content. Chromium increased erythrocyte count in lambs fed HP (Cr x CP, P < .08), and isolated peripheral lymphocytes had greater blastogenic response to 4 microg/mL of phytohemagglutinin (Cr x CP, P < .001). The lymphocyte response to pokeweed mitogen (.2 microg/mL) was reduced in lambs fed Cr (P < .10). In the present experiment, Cr supplementation had minimal and inconsistent effects on production and metabolic criteria of lambs.
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Carrion-Vazquez M, Oberhauser AF, Fowler SB, Marszalek PE, Broedel SE, Clarke J, Fernandez JM. Mechanical and chemical unfolding of a single protein: a comparison. Proc Natl Acad Sci U S A 1999; 96:3694-9. [PMID: 10097099 PMCID: PMC22356 DOI: 10.1073/pnas.96.7.3694] [Citation(s) in RCA: 777] [Impact Index Per Article: 31.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Is the mechanical unraveling of protein domains by atomic force microscopy (AFM) just a technological feat or a true measurement of their unfolding? By engineering a protein made of tandem repeats of identical Ig modules, we were able to get explicit AFM data on the unfolding rate of a single protein domain that can be accurately extrapolated to zero force. We compare this with chemical unfolding rates for untethered modules extrapolated to 0 M denaturant. The unfolding rates obtained by the two methods are the same. Furthermore, the transition state for unfolding appears at the same position on the folding pathway when assessed by either method. These results indicate that mechanical unfolding of a single protein by AFM does indeed reflect the same event that is observed in traditional unfolding experiments. The way is now open for the extensive use of AFM to measure folding reactions at the single-molecule level. Single-molecule AFM recordings have the added advantage that they define the reaction coordinate and expose rare unfolding events that cannot be observed in the absence of chemical denaturants.
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