Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.2.1.108 (lactase)
 2,133 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A key aspect in the structure of epithelial and neuronal cells is the maintenance of a polarized organization based on highly specific sorting machinery at the exit site of the trans Golgi network (TGN). Epithelial cells sort protein and lipid components into different sets of carriers for the apical or basolateral plasma membrane. The two intestinal proteins lactase-phlorizin hydrolase (LPH) and sucrase-isomaltase (SI) are delivered to the apical plasma membrane of epithelial cells with high fidelity but differ in their affinity to detergent-insoluble, glycolipid-enriched complexes (DIGs). Using a two-color labeling technique, we have recently characterized two post-Golgi vesicle populations that direct LPH and SI separately to the apical cell surface. Here, we investigated the structure and identification of protein components in these vesicle populations and assessed the role of cytoskeletal post-Golgi transport routes for apical cargo. Apart from the central role of microtubules in vesicle transport, we demonstrate that the transport of SI-carrying apical vesicles (SAVs) occurs along actin tracks in the cellular periphery, whereas LPH-carrying apical vesicles (LAVs) are transferred in an actin-independent fashion to the apical membrane. Our data further indicate that myosin 1A is the actin-associated motor protein that drives SAVs along actin filaments to the apical cell surface.
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PMID:Distinct cytoskeletal tracks direct individual vesicle populations to the apical membrane of epithelial cells. 1267 94

A key aspect in the structure of epithelial cells is the maintenance of a polarized organization based on a highly specific sorting machinery for cargo destined for the apical or the basolateral membrane domain at the exit site of the trans-Golgi network. We could recently identify two distinct post-trans-Golgi network vesicle populations that travel along separate routes to the plasma membrane, a lipid raft-dependent and a lipid raft-independent pathway. A new component of raft-carrying apical vesicles is alpha-kinase 1 (ALPK1), which was identified in immunoisolated vesicles carrying raft-associated sucrase-isomaltase (SI). This kinase was absent from vesicles carrying raft-non-associated lactase-phlorizin hydrolase. The expression of ALPK1 increases by the time of epithelial cell differentiation, whereas the intracellular localization of ALPK1 on apical transport vesicles was confirmed by confocal analysis. A phosphorylation assay on isolated SI-carrying vesicles revealed the phosphorylation of a protein band of about 105 kDa, which could be identified as the motor protein myosin I. Finally, a specific reduction of ALPK1-expression by RNA interference results in a significant decrease in the apical delivery of SI. Taken together, our data suggest that the phosphorylation of myosin I by ALPK1 is an essential process in the apical trafficking of raft-associated SI.
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PMID:Alpha-kinase 1, a new component in apical protein transport. 1588 61