Biomedical subjects
Publications and source records attributed to G S Huang.
This article describes two cases of juxta-articular osteoid osteoma of talar neck. Both patients were initially treated as having ankle sprains or arthritis before diagnosis of osteoid osteoma. A high index of suspicion and appropriate imaging studies are important to make an early diagnosis of this disorder. Once diagnosis is confirmed, en bloc resection and autogenous bone graft can cure the disorder.
A moderately stable protein with typical folding kinetics unfolds and refolds many times during its cellular lifetime. In monomeric lambda repressor this process is extremely rapid, with an average folded state lifetime of only 30 milliseconds. A thermostable variant of this protein (G46A/G48A) unfolds with the wild-type rate, but it folds in approximately 20 microseconds making it the fastest-folding protein yet observed. The effects of alanine to glycine substitutions on the folding and unfolding rate constants of the G46A/G48A variant, measured by dynamic NMR spectroscopy, indicate that the transition state is an ensemble comprised of a disperse range of conformations. This structural diversity in the transition state is consistent with the idea that folding chains are directed towards the native state by a smooth funnel-like conformational energy landscape. The kinetic data for the folding of monomeric lambda repressor can be understood by merging the new energy landscape view of folding with traditional models. This hybrid model incorporates the conformational diversity of denatured and transition state ensembles, a transition state activation energy, and the importance of intrinsic helical stabilities.
Dynamic NMR methods have been employed to measure the folding and unfolding rate constants of two extremely fast-folding proteins. lambda 6-85, a truncated, monomeric form of the N-terminal domain of lambda repressor, refolds with a lifetime of approximately 250 microseconds. These methods have also been applied to a thermostable lambda 6-85 variant with alanine substituted for glycine residues 46 and 48 in the third helix (G46A/G48A). Both proteins exhibit linear ln (kf,u) versus [urea] plots, consistent with two-state folding for both proteins. When extrapolated to 0M urea, the data indicate that G46A/G48A folds with a lifetime of less than 20 microseconds. The slopes of the ln (kf,u) versus [urea] curves (mu and mf) indicate that the modest Gly-->Ala double mutation dramatically changes the transition state solvent accessibility. The transition state for lambda 6-85 has a fractional accessibility (mu/(mu-mf)) of 0.61, whereas the transition state for G46A/G48A is much more native-like, with a fractional accessibility of 0.16. The extraordinary change in the folding pathway that these mutations induce suggests that the intrinsic stability of helix 3 is an important determinant of the folding mechanism.
The study of habituation in animals with relatively simple nervous systems has contributed significantly to the understanding of mechanisms underlying learning and memory. Using the tail-elicited siphon withdrawal reflex of Aplysia, which is mediated in part by bilaterally symmetrical clusters of tail sensory neurons, we found that both short-term and long-term habituation can be restricted laterally, such that habituation produced by stimulation of one side of the tail does not generalize to the other side. Further experiments in this preparation revealed that long-term, laterally restricted habituation is sensitive to the temporal pattern with which stimuli are presented. We also determined that both short-term and long-term habituation can take place in a reduced behavioral preparation, and that short-term habituation can be restricted within relatively small stimulation sites located on the same side of the tail. These results provide insights into the cellular organization of habituation, and they provide a useful preparation for a cellular analysis of this basic form of learning.
Although the denaturation of proteins by low temperatures is a well-documented phenomenon, little is known about the molecular details of the process. In this study, the parameters describing the denaturation thermodynamics of residues 6-85 of the N-terminal domain of lambda repressor have been determined by fitting the three-dimensional thermal-urea denaturation surface obtained by circular dichroism. The shape of the surface shows cold denaturation at low temperatures and urea concentrations above 2 M, which allows accurate determination of the apparent heat capacity of denaturation (delta Cp). Denaturation curves based on aromatic 1H NMR spectra give identical denaturation curves, confirming purely twostate folding under all conditions studies. The denaturation surface can be fit with constant delta Cp and delta In KD/delta[urea] (KD is the equilibrium constant for denaturation), consistent with a thermodynamically invariant denatured state. In addition, the aromatic 1H NMR spectrum of the cold denatured state at 0 degree C in 3 M uea is essentially identical to the spectrum at 70 degree C in 3 M urea. These observations indicate that the structures of the cold and heat denatured states, in the presence of 3 M urea, are thermodynamically and conformationally equivalent.
Bcl-2 (B cell leukemia/lymphoma-2), one of apoptosis-suppressing genes, can inhibit apoptosis of both some normal and tumor cells, and is related to the development of some tumors. In present study, the expression of bcl-2 was examined in 26 cases of oral lymphomas of mucosa associated lymphoid tissue (LMALT) using immunohistochemistry. The results showed that 73% of LMALT were positive to bcl-2 antibody. Among three main histological subtypes, the small-cleaved cell type demonstrated highest positive persentage (83%), followed by lymphoplasmacytoid lymphoma (71%) and lymphoplasmacytic lymphoma (51%). In respect to immunological subtypes, bcl-2 was detected in 69% of B cell lymphoma, 75% of T cell lymphoma, and 83% of lymphomas which could not be classified by present immunohistochemistry repectively. The results indicated that the inhibition of apoptosis might not be one of reasons for the development of some LMALT.
The folding kinetics of a truncated form of the N-terminal domain of phage lambda repressor [lambda 6-85] has been investigated by using the technique of dynamic NMR. lambda 6-85 has been shown previously to fold in a purely two-state fashion. This allows the determination of folding and unfolding rates from simulation of the exchange-broadened aromatic resonances of Tyr-22. The folding kinetics were determined over a range of 1.35 to 3.14 M urea. The urea dependence of both folding and unfolding rate constants is exponential, suggesting that the rate-determining step is invariant at the urea concentrations studied. The folding and unfolding rates extrapolated to 0 M urea at 37 degrees C are 3600 +/- 400 s-1 and 27 +/- 6 s-1, respectively. The observed lambda 6-85 folding rate constant exceeds that of other fast-folding globular proteins by a factor of 14-54. The urea dependence of the folding and unfolding rate constants suggests that the transition state of the rate-determining step is considerably more exposed to solvent than previously studied protein-folding transition states. The surprising rapidity of lambda 6-85 folding and unfolding may be the consequence of its all-helical secondary structure. These kinetic results clearly demonstrate that all of the fundamental events of protein folding can occur on the submillisecond time scale.
The absence of equilibrium intermediates in protein folding reactions (i.e., two-state folding) simplifies thermodynamic and kinetic analyses but is difficult to prove rigorously. We demonstrate a sensitive method for detecting partially folded species based on using proton chemical shifts as local probes of structure. The coincidence of denaturation curves for probes throughout the molecule is a particularly stringent test for two-state folding. In this study we investigate a new form of the N-terminal domain of bacteriophage lambda repressor consisting of residues 6-85 (lambda 6-85) using nuclear magnetic resonance (NMR) and circular dichroism (CD). This truncated version lacks the residues required for dimerization and is monomeric under the conditions used for NMR. Heteronuclear NMR was used to assign the 1H, 15N, and backbone 13C resonances. The secondary and tertiary structure of lambda 6-85 is very similar to that reported for the crystal structure of the DNA-bound 1-92 fragment [Beamer, L. J., and Pabo, C. O. (1992) J. Mol. Biol. 227, 177-196], as judged by analysis of chemical shifts, amide hydrogen exchange, amide-alpha coupling constants, and nuclear Overhauser enhancements. Thermal and urea denaturation studies were conducted using the chemical shifts of the four aromatic side chains as local probes and the CD signal at 222 nm as a global probe. Plots of the fraction denatured versus denaturant concentration obtained from these studies are identical for all probes under all conditions studied. This observation provides strong evidence for two-state folding, indicating that there are no populated intermediates in the folding of lambda 6-85.
When inserted at novel locations in the yeast genome, the Saccharomyces cerevisiae recombination hotspot HOT1 stimulates mitotic exchange in adjacent sequences. HOT1 is derived from the rDNA repeat unit, and the sequences required for the recombination-stimulatory activity closely correspond to the rDNA transcription enhancer and initiation site, suggesting there is an association between high levels of RNA polymerase I transcription and increased recombination. To directly test whether RNA polymerase I is essential for HOT1 activity, a subunit of RNA polymerase I was deleted in a strain in which rRNA is transcribed by RNA polymerase II. HOT1 is completely inactive in this strain. Deletion analysis and site-directed mutagenesis were used to further define the sequences within the rDNA enhancer required for HOT1 activity. These studies show that the enhancer contains at least four distinct regions that are required for hotspot activity. In most cases mutations in these regions also decrease transcription from this element, further confirming the association of recombination and transcription.
A patient with ankylosing spondylitis and coexisting IgA nephropathy and leukocytoclastic cutaneous vasculitis is described. Renal biopsy demonstrated mesangial proliferative glomerulonephritis with prominent IgA, C3 and fibrin deposition in the glomeruli. Simultaneously, leukocytoclastic cutaneous vasculitis with prominent IgG, IgA and C3 deposition of dermal vessel wall was also observed in the skin biopsy specimen. Such associations have been previously reported in only four cases. This report once again indicates that antigenic mucosal stimulation may play an important role in the pathogenesis of ankylosing spondylitis.
We applied more sensitive immunohistochemical method, i.e. multilayered PAP, to investigate the expression and distribution of apoptosis-antagonizing gene bcl-2 in Hodgkin's disease (HD), bcl-2-positive Reed-Sternberg (RS) cells were found in 7 of 21 (33%) of HD, and 2 of 7 (mixed cellularity) accompanied by a lot of reactive lymphoid follicles, the germinal centers of which were also positive for bcl-2. In contrast, in 4 cases of inflammatory lymphoid follicular hyperplasia as positive controls, the mantle zones rich in long-lived B cells were strongly positive stained with bcl-2 antibody, whereas germinal centers were negative. Thus, our data indicate that overexpressed bcl-2 gene-mediated apoptosis impairment is strongly associated with pathogenesis of HD.
The sesamoid bones of the first metatarsal exhibit a special anatomic configuration, enveloped by the tendons of the flexor hallucis brevis and lying within the capsule of the first metatarsophalangeal joint. Painful conditions of the hallux sesamoid bones are many and include congenital, traumatic, arthritic, infectious, and ischemic conditions. Because of the complex anatomy and the numerous pain-sensitive structures in the region of the first metatarsophalangeal joint, a differential diagnosis can be challenging. The imaging examination should always begin with conventional radiography, including special axial and lateromedial views of the sesamoid bones. In cases in which results of routine radiography are inconclusive, scintigraphy, conventional or computed tomography, xeroradiography, or magnetic resonance imaging can be used. A thorough understanding of the anatomy; pathophysiology; and clinical, laboratory, and imaging findings is often helpful in the establishment of a diagnosis and management plan for painful conditions of the hallux sesamoid bones.
The orientation of the intervertebral foramina (IVF) at six cervical levels on transaxial images in 65 magnetic resonance (MR) studies was determined to explain variations in size and shape evident on the 45 degrees standard radiographic oblique view. Analysis of MR imaging data showed that substantial variations in the orientation of the cervical IVFs occurred throughout the cervical spine and that a 55 degrees anteroposterior (AP) oblique view with standard radiography probably would lead to better visualization of the lower cervical IVFs. These results were confirmed with a radiographic and anatomic study of two cadaveric specimens. In a prospective clinical study of 23 patients, 45 degrees and 55 degrees AP oblique views were compared by measuring the maximal transverse diameter of all the cervical IVFs. IVF size was substantially increased on the 55 degrees AP oblique projection at all lower cervical levels. The 55 degrees AP oblique view of the cervical spine is optimal for evaluating the lower cervical foramina and can be a routine alternative to the 45 degrees oblique view in the analysis of all cervical foramina.
To clarify the characteristics, extent, and frequency of spinal ossification and abnormalities of the sacroiliac joint, symphysis pubis, and hip in paralysis, routine radiographs of the lumbar spine, pelvis, and abdomen were retrospectively evaluated in 95 quadriplegic, 105 paraplegic, and 100 age-matched control patients, with attention to age and race and to spinal level and duration of paralysis. The spinal radiographs were evaluated for presence of osteophytes, syndesmophytes, paravertebral ossification, and flowing hyperostosis characteristic of diffuse idiopathic skeletal hyperostosis (DISH); the pelvic radiographs were used to measure the widths of the sacroiliac joint, hip, and symphysis pubis articulations and evaluate for presence of enthesopathy. Bone formation around vertebral bodies was often seen in quadriplegic (n = 41 [43%]) and paraplegic (n = 46 [44%]) patients. In quadriplegic patients, four distinct vertebral ossification patterns were evident: osteophytosis, paraspinal ossification resembling that found in psoriasis, syndesmophytosis, and flowing ossification similar to that in DISH. In paraplegic patients, osteophytosis was most frequent. Vertebral ossification in quadriplegic patients was significantly associated with age (P < .01) and increased in frequency and severity with increasing age.
OBJECTIVE: Costal hyperostosis occurring with vertebral disorders, although not well known, has been described in patients with diffuse idiopathic skeletal hyperostosis (DISH). Our purpose was to examine the possible association of similar hyperostosis in other spinal conditions. METHODS: We investigated the frequency of hyperostotic rib changes on routine radiographs in 191 patients with various spinal disorders, including DISH (51 cases), ankylosing spondylitis (AS) (58 cases), psoriasis (21 cases) and quadriplegia (61 cases), and in a healthy control group (191 cases). RESULTS: Results showed that the frequency of rib hyperostosis was significantly higher in DISH (21.6%), AS (10.3%) and quadriplegia (6.6%) than in the healthy control group (0.5%). There was no significant difference in the frequency of right and left-sided involvement. The main radiographic features were a short segment of cortical thickening and sclerosis, which predominated in the medial aspect of the posterior portion of the rib. Some patients had a long segment of bone enlargement and extensive sclerosis. The resulting radiographic features simulated the appearance of Paget's disease. Osseous excrescences of adjacent costovertebral articulations were significantly related to the rib hyperostosis, seen in 73% of instances of rib involvement. CONCLUSION: Our observations suggest that diseases that lead to bone formation and resultant hypomobility of costovertebral articulations are associated with rib hyperostosis.
OBJECTIVE: To correlate the radiographic and pathologic findings in calcium pyrophosphate dihydrate (CPPD) crystal deposition disease and the pseudogout syndrome in the acromioclavicular (AC) joint, a relatively infrequent, but clinically important site. METHODS: We describe a case with a definite diagnosis of CPPD crystal deposition leading to pseudogout of the AC joint. We also identified 17 other patients with CPPD crystal deposition disease who showed intraarticular or periarticular calcification in this joint and investigated the radiographic findings in 26 AC joints in these 17 patients. We then correlated the results with the pathologic findings in 2 cadavers with AC joint manifestations of the disease. RESULTS: Intradiscal calcification, mainly linear or punctate in configuration, was found between adjacent bony margins in 9 of 26 AC joints (35%) or between the bony margins and extending above the upper articular bony margin in 14 AC joints (54%). Two joints (8%) showed diffuse calcification within the discs between, above, and below the articular bony margins. The remaining joint (3%) had intradiscal calcification only above the upper bony margins of the AC joint. All the joints with calcifications above the articular margins had associated globular or tumor-like soft tissue masses. A pseudogout attack at the AC joint may have nonspecific shoulder pain as its presenting symptom. CONCLUSION: CPPD crystal deposition disease leading to pseudogout syndrome of the AC joint is a clinically significant condition. We emphasize that careful assessment of the AC joint and adjacent soft tissue using intensive bright light on routine shoulder radiographs may increase the sensitivity of detecting discal and capsular calcifications in patients with pseudogout of the shoulder.
Thalamic hemorrhage or infarction is one of the common causes of stroke. People who suffer from this type of cerebrovascular disease may develop thalamic syndrome which includes sensory disturbance, motor deficit and psychological problems. In this report, we introduce two cases of thalamic hemorrhage followed up for more than a half year after stroke. Delayed rigidity and choreodystonic type of involuntary movement over their paretic hand developed gradually. The metacarpophalangeal joints of the affected hand were kept flexed and the proximal and distal interphalangeal joints became extended. Thalamic hand is demonstrated in the appended pictures. Once the patient develops a thalamic hand, activities of daily living will be affected due to poor hand performance despite of high motor recovery stage. Early recognition and proper rehabilitation program for the patients with thalamic hand are emphasized.
Soft tissue chondromas are relatively rare benign tumors, while as osseous chondromas are more commonly found. Although these tumors resemble many other soft tissue lesions, they can usually be differentiated. A review of literature is presented, and clinical manifestations and roentgenographic features are also discussed. An important point to note is that this tumor is benign and spares the patient unnecessary radical therapy.