GFP chimeras of E-MAP-115 (ensconsin) domains mimic behavior of the endogenous protein in vitro and in vivo

Cell Struct Funct. 1999 Oct;24(5):313-20. doi: 10.1247/csf.24.313.

Abstract

E-MAP-115 (ensconsin) is a microtubule-associated protein (MAP) abundant in carcinoma and other epithelia-derived cells. We expressed chimeras of green fluorescent protein (GFP) conjugated to ensconsin's N-terminal MT-binding domain (EMTB), to study distribution, dynamics, and function of the MAP in living cells. We tested the hypothesis that behavior of expressed GFP-EMTB accurately matched behavior of endogenous ensconsin. Like endogenous MAP, GFP-EMTB was associated with microtubules in living or fixed cells, and microtubule association of either molecule was impervious to extraction with nonionic detergents. In cell lysates both GFP-EMTB and endogenous ensconsin were dissociated from microtubules by identical salt extraction conditions, and both molecules remained bound to a calcium-stable subset of Taxol-stabilized microtubules. These data show that microtubule association of ensconsin was affected neither by the absence of domains other than its microtubule-binding domain, nor by the presence of appended GFP. We took advantage of this finding to generate constructs in which additional GFP moieties were attached to EMTB, to obtain a more intensely fluorescent reporter of in vivo MAP binding. We show here that expression of chimeric proteins consisting of five GFP molecules attached to a single EMTB molecule produces brightly labeled microtubules without compromising the behavior of the MAP or the microtubules to which it is attached. Thus, we have demonstrated the utility of chimeric proteins containing GFP multimers as authentic reporters of ensconsin distribution and dynamics; expression of these GFP-EMTB chimeric molecules also provides a non-perturbing label of the microtubule system in living cells.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Blotting, Western
  • Calcium / chemistry
  • Cell Line
  • Gene Expression Regulation
  • Genetic Vectors / genetics
  • Green Fluorescent Proteins
  • HeLa Cells
  • Humans
  • Luminescent Measurements
  • Luminescent Proteins / genetics
  • Luminescent Proteins / metabolism*
  • Microscopy, Fluorescence
  • Microtubule-Associated Proteins / genetics
  • Microtubule-Associated Proteins / metabolism*
  • Microtubules / chemistry
  • Microtubules / metabolism
  • Paclitaxel / chemistry
  • Protein Binding
  • Recombinant Fusion Proteins / chemistry
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism*
  • Transfection

Substances

  • Luminescent Proteins
  • Microtubule-Associated Proteins
  • Recombinant Fusion Proteins
  • epithelial microtubule-associate protein, 115 kDa
  • Green Fluorescent Proteins
  • Paclitaxel
  • Calcium