Biomedical subjects

Ramon L Serrano

Publications and source records attributed to Ramon L Serrano.

4 recordsLinked to original sources

PubMed2006

TIP47 is a key effector for Rab9 localization.

The human genome encodes approximately 70 Rab GTPases that localize to the surfaces of distinct membrane compartments. To investigate the mechanism of Rab localization, chimeras containing heterologous Rab hypervariable domains were generated, and their ability to bind seven Rab effectors was quantified. Two chimeras could bind effectors for two distinctly localized Rabs; a Rab5/9 hybrid bound both Rab5 and Rab9 effectors, and a Rab1/9 hybrid bound to certain Rab1 and Rab9 effectors. These unusual chimeras permitted a test of the importance of effector binding for Rab localization. In both cases, changing the cellular concentration of a key Rab9 effector, which is called tail-interacting protein of 47 kD, moved a fraction of the proteins from their parental Rab localization to that of Rab9. Thus, relative concentrations of certain competing effectors could determine a chimera's localization. These data confirm the importance of effector interactions for Rab9 localization, and support a model in which effector proteins rely on Rabs as much as Rabs rely on effectors to achieve their correct steady state localizations.

Binding, Competitive↗

PubMed2004

Structural analysis of the human Golgi-associated plant pathogenesis related protein GAPR-1 implicates dimerization as a regulatory mechanism.

The plant pathogenesis related proteins group 1 (PR-1) and a variety of related mammalian proteins constitute a PR-1 protein family that share sequence and structural similarities. GAPR-1 is a unique family member as thus far it is the only PR-1 family member that is not co-translationally targeted to the lumen of the endoplasmic reticulum before trafficking to either vacuoles or secretion. Here we report that GAPR-1 may form dimers in vitro and in vivo, as determined by yeast two-hybrid screening, biochemical and biophysical assays. The 1.55A crystal structure demonstrates that GAPR-1 is structurally homologous to the other PR-1 family members previously solved (p14a and Ves V 5). Through an examination of inter-molecular interactions between GAPR-1 molecules in the crystal lattice, we propose a number of the highly conserved amino acid residues of the PR-1 family to be involved in the regulation of dimer formation of GAPR-1 with potential implications for other PR-1 family members. We show that mutagenesis of these conserved amino acid residues leads to a greatly increased dimer population. A recent report suggests that PR-1 family members may exhibit serine protease activity and further examination of the dimer interface of GAPR-1 indicates that a catalytic triad similar to that of serine proteases may be formed across the dimer interface by residues from both molecules within the dimer.

Amino Acid Sequence↗

PubMed2004

Crystallization of a Golgi-associated PR-1-related protein (GAPR-1) that localizes to lipid-enriched microdomains.

The human Golgi-associated PR-1-related protein (GAPR-1) is closely related to plant pathogenesis-related (PR-1) proteins, which are upregulated in response to pathogen attack. Family members have been identified in a variety of organisms, together constituting the superfamily of PR-1 proteins. GAPR-1 is found within lipid-enriched microdomains on the cytosolic side of the endomembrane system. GAPR-1 is tightly anchored to membranes and absent from the cytosol, although it does not possess a membrane-spanning domain. Crystals of recombinantly expressed GAPR-1 have been grown that diffract to high (1.5 A) resolution. Complete data sets have been collected on a trigonal crystal form (P3(1)21/P3(2)21), with unit-cell parameters a = b = 73.5, c = 63.2 A. Molecular replacement using the NMR coordinates of tomato pathogenesis-related protein (28% identity) was unsuccessful and a search for heavy-metal derivatives or alternative phasing methods has been initiated.

Cloning, Molecular↗

PubMed2002

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.

Amino Acid Sequence↗