Identification and characterization of a novel human plant pathogenesis-related protein that localizes to lipid-enriched microdomains in the Golgi complex.
Group 1 of plant pathogenesis-related proteins (PR-1) and a variety of related mammalian proteins constitute a superfamily of proteins that share structural similarities. Little is known about their function, but all the family members identified to date are co-translationally translocated to the lumen of the endoplasmic reticulum and are secreted as soluble proteins or are targeted to vacuoles. Here we report the identification of a novel family member that localizes to the cytosolic site of the endomembrane system in mammalian cells. After detergent solubilization of isolated Golgi membranes, a 17 kDa protein was found associated with a low-density detergent-insoluble fraction. The amino-acid sequence, determined by microsequencing and molecular cloning, revealed a significant homology with the superfamily of PR-1 proteins. Golgi-associated PR-1 protein (GAPR-1) showed a brefeldin-A-sensitive Golgi localization in immunofluorescence. Interestingly, the protein remained associated with the microdomain fraction in the presence of Brefeldin A. By mass spectrometry, GAPR-1 was shown to be myristoylated. Immunoprecipitation of GAPR- 1 from Golgi membranes resulted in the coimmunoprecipitation of caveolin-1, indicating a direct interaction between these two proteins. Myristoylation, together with protein-protein or electrostatic interactions at physiological pH owing to the highly basic pI of GAPR-1 (pI 9.4) could explain the strong membrane association of GAPR-1. Tissue screening revealed that GAPR-1 is not detectably expressed in liver, heart or adrenal glands. High expression was found in monocytes, leukocytes, lung, spleen and embryonic tissue. Consistent with the involvement of PR-1 proteins in the plant immune system, these data could indicate that GAPR-1 is involved in the immune system.
Eberle
Heike B
HB
Biochemie-Zentrum Heidelberg (BZH), University of Heidelberg, Im Neuenheimer Feld 328, 69120 Heidelberg, Germany.
Serrano
Ramon L
RL
Füllekrug
Joachim
J
Schlosser
Andreas
A
Lehmann
Wolf D
WD
Lottspeich
Friedrich
F
Kaloyanova
Dora
D
Wieland
Felix T
FT
Helms
J Bernd
JB
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D020126:Brefeldin A / Q000494:pharmacology; D016466:CHO Cells; D051242:Caveolin 1; D022461:Caveolins / Q000032:analysis; D006224:Cricetinae; D003600:Cytosol / Q000737:chemistry; D005260:Female; D006056:Golgi Apparatus / Q000737:chemistry*; D006801:Humans; D008297:Male; D021962:Membrane Microdomains / Q000737:chemistry*; D008565:Membrane Proteins / Q000032:analysis* / Q000235:genetics*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010940:Plant Proteins / Q000235:genetics*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D051381:Rats; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D014018:Tissue Distribution
C495540:CAV1 protein, human; C495537:Cav1 protein, rat; D051242:Caveolin 1; D022461:Caveolins; C458481:GLIPR2 protein, human; D008565:Membrane Proteins; D010940:Plant Proteins; D011500:Protein Synthesis Inhibitors; C053376:pathogenesis-related proteins, plant; D020126:Brefeldin A