Disease relevance of KEX1

• A vaccinia virus vector was used to express the yeast KEX1 gene, which encodes a prohormone carboxypeptidase specific for the removal of basic amino acids from prohormone processing intermediates, in mammalian cells [1].
• The resulting truncated KEX1 gene (KEX1 delta) has been expressed in the baculovirus/insect cell system [2].

High impact information on KEX1

• The predicted amino acid sequence of the "protective protein" bears homology to yeast carboxypeptidase Y and the KEX1 gene product [3].
• A mutant replacing serine at the putative active site of the KEX1 protein abolished activity in vivo [4].
• Kex2 and Kex1 may promote cell fusion by proteolytically processing substrates that act in parallel to Prm1 as an alternative fusion machine, as cell wall components, or both [5].
• Kre2p/Mnt1p is localized in a Golgi compartment that overlaps with that containing the medial-Golgi mannosyltransferase Mnn1p, and distinct from that including the late Golgi protein Kex1p [6].
• Glycosylation studies of Kex1p were consistent with a Golgi location, as Kex1p was progressively N-glycosylated in an MNN1-dependent manner [7].

Biological context of KEX1

• The KEX1 gene of K. lactis has been cloned by complementation of kex1 mutations by using a recombinant plasmid pool containing the entire Kluyveromyces lactis genome, on a multicopy plasmid KEp6, which contains the Saccharomyces cerevisiae URA3 gene as a marker [8].
• The cloned KEX1 gene of K. lactis has low but significant sequence homology with the KEX2 gene of Saccharomyces cerevisiae [8].
• Kex1 is located on chromosome VII between ade5 and lys5 [9].
• K. lactis diploids homozygous for kex1 are deficient for sporulation [8].
• We present data on the Kex1p and Kex2p enzymes, their cellular localization, and their post-translational modification [10].

Anatomical context of KEX1

• To address the basis of Kex1p targeting to the Golgi apparatus, we examined the cellular location of a series of carboxy-terminal truncations of the protein [7].
• The method gives a high yield of sealed organelles that are essentially free of contamination from other secretory pathway organelles while being significantly enriched for two other late Golgi enzymes, dipeptidylaminopeptidase A and the Kex1 carboxypeptidase [11].
• The mature C terminus of the beta subunit is trimmed by Kex1p, which removes the terminal Arg(345) residue, thus uncovering the toxin's endoplasmic reticulum targeting signal (HDEL) which--in a sensitive target cell--is essential for retrograde toxin transport [12].

Associations of KEX1 with chemical compounds

• Our results provide biochemical evidence consistent with earlier genetic work, that KEX1 encodes a serine carboxypeptidase involved in the processing of precursors to secreted mature proteins [13].
• Kex2 is located on chromosome XIV, but it does not show meiotic linkage to any gene previously located on this chromosome.--When the killer plasmid of kex1 or kex2 strains is eliminated by curing with heat or cycloheximide, the strains become sensitive to killing [9].
• We hypothesized that the KEX1 homologue in P. pastoris is responsible for the loss of the C-terminal lysine of endostatin [14].
• Kex1p was found to be a membrane-associated glycoprotein with N-linked carbohydrate [13].
• We demonstrate that Kex1 contributes also to the active cell death program induced by acetic acid stress or during chronological aging, suggesting that Kex1 plays a more general role in cellular suicide of yeast [15].

Other interactions of KEX1

• Maturation of the alpha-factor precursor involves three proteolytic activities which are encoded by the KEX1, KEX2, and STE13 genes, respectively [16].
• Direct involvement of yscY and ysc alpha was confirmed by sequential disruption of their structural genes PRC1 and KEX1, respectively [17].
• The clathrin heavy chain gene was mapped 1-2 cM distal to KEX1 on the left arm of chromosome VII by making use of integrated 2 mu plasmid sequences to destabilize distal chromosome segments and allow ordering of the genes [18].
• Combination of mutations and disruptions of the host genes encoding proteinase A, B, carboxypeptidase Y, and Kex1p or Mkc7p did not influence the C-terminal deletions [19].

Analytical, diagnostic and therapeutic context of KEX1

• Site-directed mutagenesis further indicated that the toxin's beta-HDEL motif ensures retrograde transport, although in a toxin-secreting yeast the beta-C-terminus is initially masked by an R residue (beta-HDELR) until Kex1p cleavage uncovers the toxin's targeting signal in a late Golgi compartment [20].
• Southern blotting of restriction enzyme digests of genomic DNA from P. carinii-infected mouse lung demonstrated that kex1 is a single copy gene [21].
• Crystallization of a soluble form of the Kex1p serine carboxypeptidase from Saccharomyces cerevisiae [22].

References