Demonstration by phase-partitioning in Triton X-114 solutions that phosphoprotein B-50 (F-1) from rat brain is an integral membrane protein

Soluble Expression and Efficient Purification of Recombinant Class I Hydrophobin DewA

Hydrophobins are small proteins (<20 kDa) with an amphipathic tertiary structure that are secreted by various filamentous fungi. Their amphipathic properties provide surfactant-like activity, leading to the formation of robust amphipathic layers at hydrophilic–hydrophobic interfaces, which make them useful for a wide variety of industrial fields spanning protein immobilization to surface functionalization. However, the industrial use of recombinant hydrophobins has been hampered due to low yield from inclusion bodies owing to the complicated process, including an auxiliary refolding step. Herein, we report the soluble expression of a recombinant class I hydrophobin DewA originating from Aspergillus nidulans, and its efficient purification from recombinant Escherichia coli. Soluble expression of the recombinant hydrophobin DewA was achieved by a tagging strategy using a systematically designed expression tag (ramp tag) that was fused to the N-terminus of DewA lacking the innate signal sequence. Highly expressed recombinant hydrophobin DewA in a soluble form was efficiently purified by a modified aqueous two-phase separation technique using isopropyl alcohol. Our approach for expression and purification of the recombinant hydrophobin DewA in E. coli shed light on the industrial production of hydrophobins from prokaryotic hosts.

Partial characterization of an approximately 20 K M(r) retinal protein whose phosphorylation is inhibited by taurine

It has been demonstrated previously that taurine (2-aminoethanesulfonic acid) is an inhibitor of protein phosphorylation in a mitochondrial fraction of the rat retina. It appears that taurine is most effective in inhibiting the phosphorylation of an approximately 20 K apparent molecular weight (M(r)) protein found in the retinal tissue. This study further characterizes the location of the approximately 20 K phosphoprotein by phase separation using Triton X-114 and also characterizes the nature of the phosphate bond by various solvent extractions and by exposure to acid and base conditions. Triton X-114 experiments indicated that the approximately 20K phosphoprotein is located in the aqueous phase and, consequently, is probably not an integral protein of the mitochondrial membranes. Treatment of the phosphoprotein with solvents, acid, and/or base determined the phosphate linkage to be through a phosphoester bond rather than an acylphosphate bond. The approximately 20 K M(r) phosphoprotein was also isolated from one-dimensional polyacrylamide gels and subsequently digested with trypsin and hydrolyzed with 1 M HCl to break all peptide bonds. Analysis of the phosphoamino acids by two-dimensional high voltage electrophoresis on cellulose plates revealed that it is both the serine and threonine residues that are phosphorylated. However, phosphorylation of the serine residue(s) is predominant.

Role of the growth-associated protein B-50/GAP-43 in neuronal plasticity

The neuronal phosphoprotein B-50/GAP-43 has been implicated in neuritogenesis during developmental stages of the nervous system and in regenerative processes and neuronal plasticity in the adult. The protein appears to be a member of a family of acidic substrates of protein kinase C (PKC) that bind calmodulin at low calcium concentrations. Two of these substrates, B-50 and neurogranin, share the primary sequence coding for the phospho- and calmodulin-binding sites and might exert similar functions in axonal and dendritic processes, respectively. In the adult brain, B-50 is exclusively located at the presynaptic membrane. During neuritogenesis in cell culture, the protein is translocated to the growth cones, i.e., into the filopodia. In view of many positive correlations between B-50 expression and neurite outgrowth and the specific localization of B-50, a role in growth cone function has been proposed. Its phosphorylation state may regulate the local intracellular free calmodulin and calcium concentrations or vice versa. Both views link the B-50 protein to processes of signal transduction and transmitter release.

Characteristics of Ca2+/calmodulin- and Ca2+/phosphatidylserine-stimulated phosphoproteins in rat striatum

The characteristics of endogenous Ca2+/calmodulin (CaM)- and Ca2+/phosphatidylserine (PS)-stimulated phosphorylated proteins in the striatum of rat were partially determined and compared in this study. The Ca2+/CaM-dependent phosphoproteins were associated with serine and threonine residues. The sensitivity of these proteins for phosphorylation by Ca2+/CaM was not affected by pretreatment of tissue with Ca2+ chelating agent, EGTA or with non-ionic detergent, Triton X-114. Triton X-114 phase separation experiments revealed that these Ca2+/CaM-dependent phosphoproteins were partitioned in the detergent rich phase suggesting that they are integral proteins of the striatal membrane. On the other hand, the Ca2+/PS-dependent phosphorylated proteins were primarily associated with the serine residue. Phosphorylation of these proteins by Ca2+/PS were abolished after the treatment with EGTA or Triton X-114. These results suggest that Ca2+/PS-dependent striatal phosphoproteins are biochemically unstable in maintaining their state of phosphorylation.

The growth-associated neuronal phosphoprotein B-50: improved purification, partial primary structure, and characterization and localization of proteolysis products

A reversed phase HPLC procedure is reported that has allowed the separation of the growth-associated, kinase C substrate protein B-50 [previously purified by isoelectric focussing (IEF)] into three components (1-, m- and rB-50). The minor form 1B-50 (probably a proteolysis product) gave a 24-residue N-terminal amino acid sequence, but the major and possibly native form (mB-50) (and also rB-50 which is probably formed during IEF) appeared to be N-terminally blocked. HPLC also separated B-60, the major proteolysis product of B-50, into three components, and the N-terminal sequence of the major B-60 was determined. HPLC peptide mapping of SAP digests of the various B-50 and B-60 protein confirmed their close relationship, and four SAP generated fragments also afforded sequence data. The amino acid sequences obtained (1B-50, B-60 and fragments) are all found in the recently predicted (based on nucleotide sequencing) B-50/GAP43 sequence (226 amino acids), further confirming the identity of B-50 and GAP43, and helping clarify the relationship of B-60 (starting at position 41 of the predicted sequence) to B-50. Correlation of amino acid analyses, SAP fragment data, and the predicted sequence provided additional information on the length of the translated products, including evidence that the N-terminus of the major (blocked) form of B-50 starts at position 1 (Met) of the predicted sequence.

Extraction of major acidic Ca2+ dependent phosphoproteins from synaptic membranes

The association of several phosphoproteins with the synaptosomal plasma membrane (SPM) was investigated by phosphorylating SPM fractions from neonatal rat brain in the presence of Ca2+ and then exposing these to a variety of agents. Extraction of the major acidic phosphoproteins, GAP-43, pp40, and pp80, was assessed by two-dimensional gel electrophoresis and fluorography. All three proteins were best extracted from the membrane by high pH and by guanidine hydrochloride. GAP-43 was not extracted in the presence of either low- or high-ionic-strength buffers, reducing agents, or chelating agents; pp80 and pp40, however, showed a significant extraction even under low-ionic-strength conditions. Partition experiments with Triton X-114 revealed an amphiphilic behavior for GAP-43 and a strong affinity for hydrophobic environments for pp80 and pp40. None of the phosphoproteins was released from the membrane by the use of a phosphatidylinositol-specific phospholipase C. The extraction properties of GAP-43, pp80, and pp40 are similar to those of known extrinsic membrane proteins and therefore suggest that these phosphoproteins are peripheral rather than integral to the membrane compartment.