Small angle X-ray scattering of resistant starch type III

Starch fraction, which is resistant to enzymatic digestion, is produced during retrogradation. This fraction, termed resistant starch type III (RSIII), has health benefits such as pre-biotic effects, improving lipid and cholesterol metabolism, and reducing the risk of colon cancer. The work presented in this paper is aimed at investigating the colloidal structure of native high amylose corn starch (HACS) and the RSIII polymorphs produced from it using small angle X-ray scattering. Experimental scattering curves were fitted with appropriate theoretical models such as the "modified lamellar model". Our results show that retrogradation at low temperature leads to formation of polymorph B with crystallinity much lower than that of the granular form, but the lamellas are arranged in long-range periodicity. Conversely, retrogradation at high temperature leads to formation of polymorphs A and V with no defined periodicity. The degree of crystallinity is very low, and the system is better described as a dilute particulate system.     

Extracellular matrix proteins modulate endocytosis of the insulin receptor

Internalization of the insulin receptor (IR) is a highly regulated multi-step process whose underlying molecular basis is not fully understood. Here we undertook to study the role of extracellular matrix (ECM) proteins in the modulation of IR internalization. Employing Chinese hamster ovary cells that overexpress IR (CHO-T cells), our results indicate that IR internalization proceeds unaffected even when Tyr phosphorylation of IR substrates, such as IRS-1, is impaired (e.g. in CHO-T cells overexpressing IRS-1 whose pleckstrin-homology domain has been deleted or in CHO-T cells that overexpress the PH/PTB domain of IRS-1). In contrast, IR internalization is affected by the context of the ECM proteins to which the cells adhere. Hence, IR internalization was inhibited 40-60% in CHO-T cells adherent onto galectin-8 (an ECM protein and an integrin ligand of the galectin family) when compared with cells adherent onto fibronectin, collagen, or laminin. Cells adherent to galectin-8 manifested a unique cytoskeletal organization, which involved formation of cortical actin and generation of F-actin microspikes that contrasted with the prominent stress-fibers formed when cells adhered to fibronectin. To better establish a role for actin filament organization in IR endocytosis, this process was assayed in CHO-T cells (adherent onto fibronectin), whose actin filaments were disrupted upon treatment with latrunculin B. Latrunculin B did not affect insulin-induced Tyr phosphorylation of IR or its ability to phosphorylate its substrates; still, a 30-50% reduction in the rate of IR internalization was observed in cells treated with latrunculin B. Treatment of cells with nocodazole, which disrupts formation of microtubules, did not affect IR internalization. These results indicate that proper actin, but not microtubular, organization is a critical requirement for IR internalization and suggest that integrin-mediated signaling pathways emitted upon cell adhesion to different extracellular matrices and the altered cytoskeletal organizations generated thereof affect the itinerary of the insulin receptor.     

Glycoprotein IIb/IIIa receptor antagonists in acute myocardial infarction and primary coronary stenting: Not always effective

Glycoprotein IIb/IIIa antagonists have been shown to be effective in reducing thrombotic complications prior to high-risk coronary interventions. Some studies have reported improved coronary flow after abciximab in slow or no-reflow phenomenon. We report a case in which abciximab did not clear the thrombotic occlusion or restore artery flow. Further studies are needed into the refractory no-flow phenomenon.     

Function of the IsiA pigment–protein complex in vivo

Photosynthesis Research - The acclimation of cyanobacterial photosynthetic apparatus to iron deficiency is crucial for their performance under limiting conditions. In many cyanobacterial species,...     

The formation of a salt bridge between helices 3 and 6 is responsible for the constitutive activity and lack of hormone responsiveness of the naturally occurring L457R mutation of the human lutropin receptor

The human lutropin receptor (hLHR) plays a pivotal role in reproductive endocrinology. A number of naturally occurring mutations of the hLHR have been identified that cause the receptor to become constitutively active. To gain further insights into the structural basis for the activation of the hLHR by activating mutations, we chose to examine a particularly strong constitutively activating mutation of this receptor, L457R, in which a leucine that is highly conserved among rhodopsin-like G protein-coupled receptors in helix 3 has been substituted with arginine. Using both disruptive as well as reciprocal mutagenesis strategies, our studies demonstrate that the ability of L457R to stabilize an active form of the hLHR is because of the formation of a salt bridge between the replacing amino acid and Asp-578 in helix 6. Such a lock between the transmembrane portions of helices 3 and 6 is concurrent with weakening the connections between the cytosolic ends of the same helices, including the interaction found in the wild-type receptor between Arg-464, of the (E/D)R(Y/W) motif, and Asp-564. This structural effect is properly marked by the increase in the solvent accessibility of selected amino acids at the cytosolic interfaces between helices 3 and 6. The integrity of the conserved amino acids Asn-615 and Asn-619 in helix 7 is required for the transfer of the structural change from the activating mutation site to the cytosolic interface between helices 3 and 6. The results of in vitro and computational experiments further suggest that the structural trigger of the constitutive activity of the L457R mutant may also be responsible for its lack of hormone responsiveness.     

Structure-Function Analysis of Nucleolin and ErbB Receptors Interactions

Background

The ErbB receptor tyrosine kinases and nucleolin are major contributors to malignant transformation. Recently we have found that cell-surface ErbB receptors interact with nucleolin via their cytoplasmic tail. Overexpression of ErbB1 and nucleolin leads to receptor phosphorylation, dimerization and anchorage independent growth.

Methodology/Principal Findings

In the present study we explored the regions of nucleolin and ErbB responsible for their interaction. Using mutational analyses, we addressed the structure–function relationship of the interaction between ErbB1 and nucleolin. We identified the ErbB1 nuclear localization domain as nucleolin interacting region. This region is important for nucleolin-associated receptor activation. Notably, though the tyrosine kinase domain is important for nucleolin-associated receptor activation, it is not involved in nucleolin/ErbB interactions. In addition, we demonstrated that the 212 c-terminal portion of nucleolin is imperative for the interaction with ErbB1 and ErbB4. This region of nucleolin is sufficient to induce ErbB1 dimerization, phosphorylation and growth in soft agar.

Conclusions/Significance

The oncogenic potential of ErbB depends on receptor levels and activation. Nucleolin affects ErbB dimerization and activation leading to enhanced cell growth. The C-terminal region of nucleolin and the ErbB1 NLS-domain mediate this interaction. Moreover, when the C-terminal 212 amino acids region of nucleolin is expressed with ErbB1, it can enhance anchorage independent cell growth. Taken together these results offer new insight into the role of ErbB1 and nucleolin interaction in malignant cells.