Pore gradient gel electrophoresis: theory, practice, and applications

ICPMS analysis of proteins separated by Native-PAGE: Evaluation of metaloprotein profiles in human synovial fluid with acute and chronic arthritis

The role of trace elements bound to proteins in the etiology and pathogenesis of rheumatoid arthritis (RA) remains unclear. In this sense, the identification and detection of metalloproteins has a strong and growing interest. Metalloprotein studies are currently carried out by polyacrylamide gel electrophoresis (PAGE) associated to inductively coupled plasma mass spectrometry (ICPMS), and despite that complete information can be obtained for metals such as Fe, Cu and Zn, difficulties due to poor sensitivity for other trace elements such as Sn, As, etc, are currently faced. In the present work, a simple and fast method for the determination of trace metals bound to synovial fluid (SF) proteins was optimized. Proteins from SF (long and short-term RA) were separated in ten fractions by native PAGE, then dissolved in nitric acid and peroxide hydrogen, and analyzed by ICPMS. Fifteen metals were determined in each separated protein fraction (band). Adequate calibration of proteins molecular weight allowed stablishing which protein type were bound to different metals.

A novel mechanism for small heat shock proteins to function as molecular chaperones

Small heat shock proteins (sHSPs) are molecular chaperones ubiquitously present in all forms of life, but their function mechanisms remain controversial. Here we show by cryo-electron microscopy and single particle 3D reconstruction that, at the low temperatures (4-25°C), CeHSP17 (a sHSP from Caenorhabditis elegans) exists as a 24-subunit spherical oligomer with tetrahedral symmetry. Our studies demonstrate that CeHSP17 forms large sheet-like super-molecular assemblies (SMAs) at the high temperatures (45-60°C), and such SMAs are apparently the form that exhibits chaperone-like activity. Our findings suggest a novel molecular mechanism for sHSPs to function as molecular chaperones.

Antioxidant status and hormonal profile reflected by experimental feeding of probiotics

Excessive production of free radicals can result in tissue damage, which mainly involves generation of hydroxyl radical and other oxidants. Such free radical-induced cell damage appears to play a major role in the pathogenesis of many diseases. Probiotics have been used therapeutically to modulate immunity, improve digestive processes, lower cholesterol, treat rheumatoid arthritis, and prevent cancer. The proposed research was designed to evaluate the changes in oxidative and antioxidative profile in addition to metabolic-related hormones of living animal model, which may generally affect the health status. Two groups of rabbits (10 animals each) were allocated in hygienic cages of controlled animal house. Control group received standard diet, and the other group received the same diet containing one probiotic for 30 days. Lactate dehydrogenase (LDH) activity in leukocytes, blood glucose, reduced glutathione (GSH), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px) were estimated in different tissues. Malondialdehyde (MDA) and total proteins were also determined in different tissues. Certain hormones related to metabolism and growth were also evaluated. Leukocytic LDH activity was significantly increased along with nonsignificant increase of blood glucose in probiotics-fed animals. Results showed significant decreases in the levels of triiodothyronine and thyroid-stimulating hormone but showed significant elevations in thyroxine, insulin, growth hormone, and testosterone levels in animals fed with probiotics. Total proteins content was highly significantly elevated in liver, kidneys, and muscles of probiotic-administered animals. Microsomal GSH level was significantly decreased only in skeletal muscles of probiotic-treated animals. MDA was significantly lowered in animal tissues fed with probiotics. GSH-Px activity was elevated in hepatic and muscular microsomes of probiotic-supplemented animals while it was nonsignificantly increased in renal microsomes. Microsomal SOD activity was elevated in liver, kidneys, and skeletal muscles of probiotics-administrated animals. It is concluded that supplementation of probiotic may enhance antioxidant efficacy and scavenge free radicals and thus may be used as a preventive measure for protection against free radicals-induced disorders.

Characterization of an intact two-component high-affinity nitrate transporter from Arabidopsis roots

AtNRT2.1, a polypeptide of the Arabidopsis thaliana two-component inducible high-affinity nitrate transport system (IHATS), is located within the plasma membrane. The monomeric form of AtNRT2.1 has been reported to be the most abundant form, and was suggested to be the form that is active in nitrate transport. Here we have used immunological and transient protoplast expression methods to demonstrate that an intact two-component complex of AtNRT2.1 and AtNAR2.1 (AtNRT3.1) is localized in the plasma membrane. A. thaliana mutants lacking AtNAR2.1 have virtually no IHATS capacity and exhibit extremely poor growth on low nitrate as the sole source of nitrogen. Near-normal growth and nitrate transport in the mutant were restored by transformation with myc-tagged AtNAR2.1 cDNA. Membrane fractions from roots of the restored myc-tagged line were solubilized in 1.5% dodecyl-β-maltoside and partially purified in the first dimension by blue native gel electrophoresis. Using anti-NRT2.1 antibodies, an oligomeric polypeptide (approximate molecular mass 150 kDa) was identified, but monomeric AtNRT2.1 was absent. This oligomer was also observed in the wild-type, and was resolved, using SDS-PAGE for the second dimension, into two polypeptides with molecular masses of approximately 48 and 26 kDa, corresponding to AtNRT2.1 and myc-tagged AtNAR2.1, respectively. This result, together with the finding that the oligomer is absent from NRT2.1 or NAR2.1 mutants, suggests that this complex, rather than monomeric AtNRT2.1, is the form that is active in IHATS nitrate transport. The molecular mass of the intact oligomer suggests that the functional unit for high-affinity nitrate influx may be a tetramer consisting of two subunits each of AtNRT2.1 and AtNAR2.1.

Enrichment and fractionation of proteins via microscale pore limit electrophoresis

In this work we photopolymerized precise and well-controlled polyacrylamide porosity gradients in microchannels for microscale pore limit electrophoresis (microPLE) of proteins. Porosity was controlled via distributions of acrylamide monomer and bisacrylamide crosslinker. MicroPLE provides high-resolution fractionation of complex samples based on the spatial dependence of each species' electrophoretic pore limit--the porosity at which a protein's electrophoretic mobility is negligible due to its molecular size. Proteins ranging in molecular weight from 21.5 kDa-144 kDa were separated under native buffering conditions along 5-mm- and 7-mm-long microPLE gels spanning 10%T, 2.6%C-40%T, 12%C. The pore gradient gel is useful for estimating size-exclusion thresholds for a broad range of polymer concentrations and protein sizes simultaneously. We show that microPLE can be used to concentrate dilute samples by exploiting the stacking phenomenon associated with an analyte's decreasing electrophoretic mobility. Concentration factors>40,000 were demonstrated with dilute (100 pM) samples. A detailed theoretical analysis of microPLE transport behavior based on Ferguson assumptions provides scaling and design parameters with which to tailor gels based on fractionation or enrichment needs. Experimental results show that the Ferguson assumptions break down as proteins migrate beyond an effective pore limit, prompting the need for further investigation into this non-Ferguson regime.

Chaperone-Like Activity of Mycobacterium tuberculosis Hsp16.3 Does Not Require Its Intact (Native) Structures

Small heat shock proteins (sHsps) were found to exhibit efficient chaperone-like activities under stress conditions although their native structures are severely disturbed. Here, using an alternative approach (site-directed mutagenesis), we obtained two structurally and functionally distinct Mycobacterium tuberculosis Hsp16.3 single-site mutant proteins. The G59W mutant protein (with Gly59 substituted by Trp) is capable of exhibiting efficient chaperone-like activity even under non-stress conditions although its secondary, tertiary, and quaternary structures are very different from that of the wild type protein. By contrast, the G59A mutant protein (with Gly59 substituted by Ala) resembles with the wild type protein in structure and function. These observations suggest that the Gly59 of the Hsp16.3 protein is critical for its folding and assembly. In particular, we propose that the exhibition of chaperone-like activity for Hsp16.3 does not require its intact (native) structures but requires the disturbance of its native structures (i.e., the native structure-disturbed Hsp16.3 retains its chaperone-like activity or even becomes more active). In addition, the behavior of such an active mutant protein (G59W) also strongly supports our previous suggestion that Hsp16.3 exhibits chaperone-like activity via oligomeric dissociation.

A dual role for the N-terminal region of Mycobacterium tuberculosis Hsp16.3 in self-oligomerization and binding denaturing substrate proteins

The N-terminal regions, which are highly variable in small heat-shock proteins, were found to be structurally disordered in all the 24 subunits of Methanococcus jannaschii Hsp16.5 oligomer and half of the 12 subunits of wheat Hsp16.9 oligomer. The structural and functional roles of the corresponding region (potentially disordered) in Mycobacterium tuberculosis Hsp16.3, existing as nonamers, were investigated in this work. The data demonstrate that the mutant Hsp16.3 protein with 35 N-terminal residues removed (DeltaN35) existed as trimers/dimers rather than as nonamers, failing to bind the hydrophobic probe (1,1'-bi(4-anilino)naphthalene-5,5'-disulfonic acid) and exhibiting no chaperone-like activity. Nevertheless, another mutant protein with the C-terminal extension (of nine residues) removed, although existing predominantly as dimers, exhibited efficient chaperone-like activity even at room temperatures, indicating that pre-existence as nonamers is not a prerequisite for its chaperone-like activity. Meanwhile, the mutant protein with both the N- and C-terminal ends removed fully exists as a dimer lacking any chaperone-like activity. Furthermore, the N-terminal region alone, either as a synthesized peptide or in fusion protein with glutathione S-transferase, was capable of interacting with denaturing proteins. These observations strongly suggest that the N-terminal region of Hsp16.3 is not only involved in self-oligomerization but also contains the critical site for substrate binding. Such a dual role for the N-terminal region would provide an effective mechanism for the small heat-shock protein to modulate its chaperone-like activity through oligomeric dissociation/reassociation. In addition, this study demonstrated that the wild-type protein was able to form heterononamers with DeltaN35 via subunit exchange at a subunit ratio of 2:1. This implies that the 35 N-terminal residues in three of the nine subunits in the wild-type nonamer are not needed for the assembly of nonamers from trimers and are thus probably structurally disordered.

Small heat shock protein Hsp16.3 modulates its chaperone activity by adjusting the rate of oligomeric dissociation

Small heat shock proteins usually exist as oligomers and appear to undergo dynamic dissociation/reassociation, with oligomeric dissociation being a prerequisite for their chaperone activities. However, contradictory cases were also reported that chaperone activities could be enhanced with no change or even increase in oligomeric sizes. Using Hsp16.3 as a model system, our studies show the following: (1) Although a preheat (over 60 degrees C) treatment or the presence of low concentrations of urea (around 0.8M) hardly caused any change in the oligomeric size of Hsp16.3 proteins when examined by size exclusion chromatography, its chaperone activities were increased significantly. (2) Further analysis using the unique pore-gradient polyacrylamide gel electrophoresis revealed a dramatic increase in the tendency of oligomeric dissociation for both the preheated and urea-containing Hsp16.3. (3) Meanwhile, for both cases, an apparent increase in the rate constants of oligomeric dissociation was also observed, as determined by utilizing conjugated fluorescence probes whose quantum yield increases accompanying oligomeric dissociation. (4) Moreover, the fluorescence anisotropy analysis also demonstrated that the oligomeric structures for the preheated or urea-containing Hsp16.3 proteins seem to be more dynamic and variable. In light of these observations, we propose that the small heat shock proteins like Hsp16.3 can modulate their chaperone activities by adjusting the rate of oligomeric dissociation in responding to environmental changes. Results obtained here also suggest that small heat shock proteins might be able to "remember" their stress experiences via certain structural alterations which will allow them to act as better chaperones when the stress conditions reappear.