Sonic hedgehog shedding results in functional activation of the solubilized protein

All Hedgehog (Hh) proteins are released from producing cells despite being synthesized as N- and C-terminally lipidated, membrane-tethered molecules. Thus, a cellular mechanism is needed for Hh solubilization. We previously suggested that a disintegrin and metalloprotease (ADAM)-mediated shedding of Sonic hedgehog (ShhNp) from its lipidated N and C termini results in protein solubilization. This finding, however, seemed at odds with the established role of N-terminal palmitoylation for ShhNp signaling activity. We now resolve this paradox by showing that N-palmitoylation of ShhNp N-terminal peptides is required for their proteolytic removal during solubilization. These peptides otherwise block ShhNp zinc coordination sites required for ShhNp binding to its receptor Patched (Ptc), explaining the essential yet indirect role of N-palmitoylation for ShhNp function. We suggest a functional model in which membrane-tethered multimeric ShhNp is at least partially autoinhibited in trans but is processed into fully active, soluble multimers upon palmitoylation-dependent cleavage of inhibitory N-terminal peptides.     

An Emerging Role of Sonic Hedgehog Shedding as a Modulator of Heparan Sulfate Interactions

Major developmental morphogens of the Hedgehog (Hh) family act at short range and long range to direct cell fate decisions in vertebrate and invertebrate tissues. To this end, Hhs are released from local sources and act at a distance on target cells that express the Hh receptor Patched. However, morphogen secretion and spreading are not passive processes because all Hhs are synthesized as dually (N- and C-terminal) lipidated proteins that firmly tether to the surface of producing cells. On the cell surface, Hhs associate with each other and with heparan sulfate (HS) proteoglycans. This raises the question of how Hh solubilization and spreading is achieved. We recently discovered that Sonic hedgehog (Shh) is solubilized by proteolytic processing (shedding) of lipidated peptide termini in vitro. Because unprocessed N termini block Patched receptor binding sites in the cluster, we further suggested that their proteolytic removal is required for simultaneous Shh activation. In this work we confirm inactivity of unprocessed protein clusters and demonstrate restored biological Shh function upon distortion or removal of N-terminal amino acids and peptides. We further show that N-terminal Shh processing targets and inactivates the HS binding Cardin-Weintraub (CW) motif, resulting in soluble Shh clusters with their HS binding capacities strongly reduced. This may explain the ability of Shh to diffuse through the HS-containing extracellular matrix, whereas other HS-binding proteins are quickly immobilized. Our in vitro findings are supported by the presence of CW-processed Shh in murine brain samples, providing the first in vivo evidence for Shh shedding and subsequent solubilization of N-terminal-truncated proteins.     

Behavior of hard X-ray emission in discharges with current disruptions in the DAMAVAND and TVD tokamaks

Results are presented from studies of the behavior of hard X-ray emission in discharges with current disruptions in the DAMAVAND and TVD tokamaks. The current disruptions are caused by either an MHD instability or the instability related to the vertical displacement of the plasma column. Experiments were conducted at a fixed value of the safety factor at the plasma boundary (q _a ? 2.3). Experimental data show that, during a disruption caused by an MHD instability, hard X-ray emission is suppressed by this instability if the amplitude of the magnetic field fluctuations exceeds a certain level. If the disruption is caused by the instability related to the vertical displacement of the plasma column, then hard X-ray emission is observed at the instant of disruption. The experimental results show that the physical processes resulting in the generation and suppression of runaway electron beams are almost identical in large and small tokamaks.     

Protein tyrosine phosphatase non-receptor type 22 gene polymorphism C1858T is not associated with leprosy in Azerbaijan,Northwest Iran

BACKGROUND:

Leprosy (Hansen''s disease) is a human chronic granulomatous infectious disease caused by Mycobacterium leprae. Several types of study support a role for host genetics in susceptibility to leprosy. The protein tyrosine phosphatase non-receptor type 22 (PTPN22) gene encodes an intracellular lymphoid protein tyrosine phosphatase that has been shown to play a negative regulatory role in T-cell activation.

AIMS:

The aim of the present study was to find out associating the PTPN22 C1858T (R620W) polymorphism and leprosy in the Azeri population from Northwest Iran.

MATERIALS AND METHODS:

A total of 153 treated leprosy patients and 197 healthy and ethnic matched controls entered this study. We used restriction fragment length polymorphism method to type PTPN22 C1858T polymorphism.

RESULTS:

There was no significant difference in distribution of genotype and allele frequencies of PTPN22 C1858T polymorphism between leprosy patients and controls (P = 0.641 and 0.645; respectively). Moreover, there was no significant association between different clinical findings (karnofsky performance status score, clinical forms and manifestations of leprosy) and PTPN22 C1858T polymorphism. Data showed a low frequency of the minor (T) allele by 2.3% in leprosy and 1.5% in healthy individuals.

CONCLUSIONS:

The PTPN22 C1858T (R620W) is not relevant in susceptibility to leprosy in the Azeri population of Northwest Iran.     

Dual roles of the Cardin-Weintraub motif in multimeric Sonic hedgehog

The fly morphogen Hedgehog (Hh) and its mammalian orthologs, Sonic, Indian, and Desert hedgehog, are secreted signaling molecules that mediate tissue patterning during embryogenesis and function in tissue homeostasis and regeneration in the adult. The function of all Hh family members is regulated at the levels of morphogen multimerization on the surface of producing cells, multimer release, multimer diffusion to target cells, and signal reception. These mechanisms are all known to depend on interactions of positively charged Hh amino acids (the Cardin-Weintraub (CW) motif) with negatively charged heparan sulfate (HS) glycosaminoglycan chains. However, a precise mechanistic understanding of these interactions is still lacking. In this work, we characterized ionic HS interactions of multimeric Sonic hedgehog (called ShhNp) as well as mutant forms lacking one or more CW residues. We found that deletion of all five CW residues as well as site-directed mutagenesis of CW residues Lys(33), Arg(35), and Lys(39) (mouse nomenclature) abolished HS binding. In contrast, CW residues Arg(34) and Lys(38) did not contribute to HS binding. Analysis and validation of Shh crystal lattice contacts provided an explanation for this finding. We demonstrate that CW residues Arg(34) and Lys(38) make contact with an acidic groove on the adjacent molecule in the multimer, suggesting a new function of these residues in ShhNp multimerization rather than HS binding. Therefore, the recombinant monomeric morphogen (called ShhN) differs in CW-dependent HS binding and biological activity from physiologically relevant ShhNp multimers, providing new explanations for functional differences observed between ShhN and ShhNp.     

Nonmonotonic Spatial Distributions of Charge-Exchange Neutral Fluxes and Optical Radiation from Plasma in the DAMAVAND Tokamak

Results are presented from investigations of the nonmonotonic spatial distributions of charge-exchange neutral fluxes and optical radiation from plasma in the DAMAVAND tokamak. It is shown that, during ohmic heating of the plasma, the regions with enhanced confinement of both the background plasma particles and heavy impurity ions arise near rational magnetic surfaces with q = 1 and 2. These regions are characterized by enhanced emission of accelerated charge-exchange neutrals and optical radiation from impurity ions.