Affinity purification of molecular chaperones of the yeast Hansenula polymorpha using immobilized denatured alcohol oxidase

The transcarboxylase domain of pyruvate carboxylase is essential for assembly of the peroxisomal flavoenzyme alcohol oxidase

Pyruvate carboxylase (Pyc1p) has multiple functions in methylotrophic yeast species. Besides its function as an enzyme, Pyc1p is required for assembly of peroxisomal alcohol oxidase (AO). Hence, Pyc1p-deficient cells share aspartate auxotrophy (Asp-) with a defect in growth on methanol as sole carbon source (Mut-). To identify regions in Hansenula polymorpha Pyc1p that are required for the function of HpPyc1p in AO assembly, a series of random mutations was generated in the HpPYC1 gene by transposon mutagenesis. Upon introduction of 18 mutant genes into the H. polymorpha PYC1 deletion strain (pyc1), four different phenotypes were obtained, namely Asp- Mut-, Asp- Mut+, Asp+ Mut-, and Asp+ Mut+. One mutant showed an Asp+ Mut- phenotype. This mutant produced HpPyc1p containing a pentapeptide insertion in the region that links the conserved N-terminal biotin carboxylation domain (BC) with the central transcarboxylation (TC) domain. Three mutants that were Asp- Mut- contained insertions in the TC domain, suggesting that this domain is important for both functions of Pyc1p. Analysis of a series of constructed C-terminal and N-terminal truncated versions of HpPyc1p showed that the TC domain of Pyc1p, including the region linking this domain to the BC domain, is essential for AO assembly.

Affinity chromatography of GroEL chaperonin based on denatured proteins: role of electrostatic interactions in regulation of GroEL affinity for protein substrates

The chaperonin GroEL of the heat shock protein family from Escherichia coli cells can bind various polypeptides lacking rigid tertiary structure and thus prevent their nonspecific association and provide for acquisition of native conformation. In the present work we studied the interaction of GroEL with six denatured proteins (alpha-lactalbumin, ribonuclease A, egg lysozyme in the presence of dithiothreitol, pepsin, beta-casein, and apocytochrome c) possessing negative or positive total charge at neutral pH values and different in hydrophobicity (affinity for a hydrophobic probe ANS). To prevent the influence of nonspecific association of non-native proteins on their interaction with GroEL and make easier the recording of the complexing, the proteins were covalently attached to BrCN-activated Sepharose. At low ionic strength (lower than 60 mM), tight binding of the negatively charged denatured proteins with GroEL (which is also negatively charged) needed relatively low concentrations (approximately 10 mM) of bivalent cations Mg2+ or Ca2+. At the high ionic strength (approximately 600 mM), a tight complex was produced also in the absence of bivalent cations. In contrast, positively charged denatured proteins tightly interacted with GroEL irrespectively of the presence of bivalent cations and ionic strength of the solution (from 20 to 600 mM). These features of GroEL interaction with positively and negatively charged denatured proteins were confirmed by polarized fluorescence (fluorescence anisotropy). The findings suggest that the affinity of GroEL for denatured proteins can be determined by the balance of hydrophobic and electrostatic interactions.

Characterization of interactions between Escherichia coli molecular chaperones and immobilized caseins

The molecular chaperones were affinity purified with immobilized alpha-casein (45mg protein/g beads) and beta-casein columns (30 mg protein/g beads) from two heat-induced E. coli strains, NM522 and BL21. After removing nonspecifically bound proteins with 1 M NaCl, the molecular chaperones were eluted with cold water, 1 mM Mg-ATP, or 6 M urea. The eluates from affinity columns were analyzed by SDS-PAGE and Western analysis. Western analysis identified five E. coli molecular chaperones including DnaK, DnaJ, GrpE, GroEL, and GroES in eluates. Among samples, ATP eluates showed the highest chaperone purity of 80-87% followed by cold water eluates with 62-68% purity. The beta-casein column showed a higher chaperone binding capacity than the alpha-casein column. A higher concentration of chaperones was purified from strain BL21 than strain NM522 which may have been due to the lack of lon protease in the BL21 strain.

Pyruvate carboxylase is an essential protein in the assembly of yeast peroxisomal oligomeric alcohol oxidase

Hansenula polymorpha ass3 mutants are characterized by the accumulation of inactive alcohol oxidase (AO) monomers in the cytosol, whereas other peroxisomal matrix proteins are normally activated and sorted to peroxisomes. These mutants also have a glutamate or aspartate requirement on minimal media. Cloning of the corresponding gene resulted in the isolation of the H. polymorpha PYC gene that encodes pyruvate carboxylase (HpPyc1p). HpPyc1p is a cytosolic, anapleurotic enzyme that replenishes the tricarboxylic acid cycle with oxaloacetate. The absence of this enzyme can be compensated by addition of aspartate or glutamate to the growth media. We show that HpPyc1p protein but not the enzyme activity is essential for import and assembly of AO. Similar results were obtained in the related yeast Pichia pastoris. In vitro studies revealed that HpPyc1p has affinity for FAD and is capable to physically interact with AO protein. These data suggest that in methylotrophic yeast pyruvate carboxylase plays a dual role in that, besides its well-characterized metabolic function as anapleurotic enzyme, the protein fulfils a specific role in the AO sorting and assembly process, possibly by mediating FAD-binding to AO monomers.

Affinity purification and characterization of the Escherichia coli molecular chaperones

The molecular chaperones are a group of proteins that are effective in vitro and in vivo folding aids and show a well-documented affinity for proteins lacking tertiary structure. The molecular chaperones were induced from lon(-) Escherichia coli mutants, affinity purified with an immobilized beta-casein column, and assayed for refolding activity with thermally and chemically denatured carbonic anhydrase B (CAB). Chaperones were induced with three treatments: heat shock at 39 degrees C, heat shock 42 degrees C, and alcohol shock with 3% ethanol (v/v). Lysates were applied to an immobilized beta-casein (30 mg/g beads) column. After removing nonspecifically bound proteins with 1 M NaCl, the molecular chaperones were eluted with cold water or 1 mM Mg-ATP. The cold water and Mg-ATP eluates were analyzed by SDS-PAGE. Western analysis identified five E. coli molecular chaperones including DnaK, DnaJ, GrpE, GroEL, and GroES. The purity of eluted chaperones was 58% with cold water and 100% with Mg-ATP. Refolding denatured CAB in the presence of Mg-ATP resulted in a 97% recovery of heat-denatured CAB and a 68% recovery of chemically denatured CAB. The use of affinity matrices for the chaperone purification which are effective as in vitro folding aids will be presented.

The glyoxysomal and plastid molecular chaperones (70-kDa heat shock protein) of watermelon cotyledons are encoded by a single gene

The monoclonal a-70-kDa heat shock protein (hsp70) antibody recognizes in crude extracts from watermelon (Citrullus vulgaris) cotyledons two hsps with molecular masses of 70 and 72 kDa. Immunocytochemistry on watermelon cotyledon tissue and on isolated glyoxysomes identified hsp70s in the matrix of glyoxysomes and plastids. Affinity purification and partial amino acid determination revealed the 70-kDa protein to share high sequence identity with cytosolic hsp70s from a number of plant species, while the 72 kDa protein was very similar to plastid hsp70s from pea and cucumber. A full-length cDNA clone encoding the 72-kDa hsp70 was isolated and identified two start methionines in frame within the N-terminal presequence leading either to an N-terminal extension of 67 amino acids or to a shorter one of 47 amino acids. The longer presequence was necessary and sufficient to target a reporter protein into watermelon proplastids in vitro. The shorter extension starting from the second methionine within the long version harbored a consensus peroxisomal targeting signal (RT-X5-KL) that directed in vivo a reporter protein into peroxisomes of the yeast Hansenula polymorpha. Peroxisomal targeting was however prevented, when the 67-residue presequence was fused to the reporter protein, indicating that the peroxisomal targeting signal 2 information is hidden in this context. We propose that the 72-kDa hsp70 is encoded by a single gene, but targeted alternatively into two organelles by the modulated use of its presequence.

Identification and characterization of cytosolic Hansenula polymorpha proteins belonging to the Hsp70 protein family

We have isolated two members of the Hsp70 protein family from the yeast Hansenula polymorpha using affinity chromatography. Both proteins were located in the cytoplasm. One of these, designated Hsp72, was inducible in nature (e.g. by heat shock). The second protein (designated Hsc74) was constitutively present. Peptides derived from both Hsp72 and Hsc74 showed sequence homology to the cytosolic Saccharomyces cerevisiae Hsp70s, Ssa1p and Ssa2p. The gene encoding Hsp72 (designated HSA1) was cloned, sequenced and used to construct HSA1 disruption and HSA1 overexpression strains. Comparison of the stress tolerances of these strains with those of wild-type H. polymorpha revealed that HSA1 overexpression negatively affected the tolerance of the cells to killing effects of temperature or ethanol, but enhanced the tolerance to copper and cadmium. The tolerance for other chemicals (arsenite, arsenate, H2O2) or to high osmolarity was unaffected by either deletion or overexpression of HSA1.