Channel reconstitution in liposomes and planar bilayers with HPLC-purified MIP26 of bovine lens

Shen, Lili; Shrager, Peter; Girsch, Stephen J.; Donaldson, Patricia J.; Peracchia, Camillo

doi:10.1007/bf01871361

Cited by 53 publications

(18 citation statements)

References 39 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Lenses were removed from fresh bovine eyes (Harris Ranch Beef, Selma, CA), rinsed in lens buffer (0.5 M NaCl͞20 mM Tris, pH 8.0͞1 mM EDTA͞0.5 mM PMSF), and decapsulated. The lenses were homogenized, stirred overnight, and washed five times by centrifugation at 125,000 ϫ g for 1 h. Even though stripping the membranes with urea and alkaline buffer (14) removes most membrane protein contaminants (15); this treatment induced AQPO oligomerization upon purification (W.E.C.H., L.J.W.M., and D.A., unpublished data) and, thus, was not performed. AQP0 was purified according to ref.…”

Section: Methodsmentioning

confidence: 99%

The channel architecture of aquaporin 0 at a 2.2-Å resolution

Harries

Akhavan

Miercke

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

252

274

View full text Add to dashboard Cite

We determined the x-ray structure of bovine aquaporin 0 (AQP0) to a resolution of 2.2 Å. The structure of this eukaryotic, integral membrane protein suggests that the selectivity of AQP0 for water transport is based on the identity and location of signature amino acid residues that are hallmarks of the water-selective arm of the AQP family of proteins. Furthermore, the channel lumen is narrowed only by two, quasi-2-fold related tyrosine side chains that might account for reduced water conductance relative to other AQPs. The channel is functionally open to the passage of water because there are eight discreet water molecules within the channel. Comparison of this structure with the recent electron-diffraction structure of the junctional form of sheep AQP0 at pH 6.0 that was interpreted as closed shows no global change in the structure of AQP0 and only small changes in side-chain positions. We observed no structural change to the channel or the molecule as a whole at pH 10, which could be interpreted as the postulated pH-gating mechanism of AQP0-mediated water transport at pH >6.5. Contrary to the electron-diffraction structure, the comparison shows no evidence of channel gating induced by association of the extracellular domains of AQP0 at pH 6.0. Our structure aids the analysis of the interaction of the extracellular domains and the possibility of a cell-cell adhesion role for AQP0. In addition, our structure illustrates the basis for formation of certain types of cataracts that are the result of mutations.T he vertebrate ocular lens is a remarkably transparent and avascular tissue that acts basically as a syncytium of differentiated epithelial cells, called fiber cells. These cells are thin and highly elongated, and they are essentially a plasma membraneenclosed sack filled with transparent crystallin proteins. The lens is covered on the surface of its anterior hemisphere with a layer of simple squamous epithelial cells and an acellular capsule that encloses the entire lens. The lack of vascular-supply structures and any identifiable active transport systems in the fiber cell mass means that diffusional pathways are of paramount importance to the establishment and maintenance of lens homeostasis and transparency. The transparency of the lens, together with its ability to undergo dynamic shape changes during accommodation, provides for a clear and accurate image of the world to be projected onto the retina. The transparent nature of the lens is contingent on several crucial features that permit light to pass through with a minimum of light scattering. These features are (i) the maintenance of a highly ordered molecular structure of the crystallin proteins; (ii) terminally differentiated fiber cells containing very few organelles; and (iii) intracellular and intercellular spaces being kept smaller than the wavelength of ambient light (1-3).It is intriguing to understand the cellular and molecular basis for the maintenance of lens transparency, as well as the loss of lens transparency due to pathological and injur...

show abstract

Section: Methodsmentioning

confidence: 99%

The channel architecture of aquaporin 0 at a 2.2-Å resolution

Harries

Akhavan

Miercke

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

252

274

View full text Add to dashboard Cite

show abstract

“…AQP0, the major protein component of isolated lens junctions, when reconstituted in bilayers has been shown to have ion channel activity (Modesto et al, 1990; Shen et al, 1991; Zampighi et al, 1985). However, other groups have reported absence of a change in ionic conductance with lens MIP expression in Xenopus oocytes (Kushmerick et al, 1995; Mulders et al, 1995).…”

Section: Aquaporin Ion Channelsmentioning

confidence: 99%

Structure, function and translational relevance of aquaporin dual water and ion channels

Yool

Campbell

2012

Molecular Aspects of Medicine

View full text Add to dashboard Cite

Aquaporins have been assumed to be selective for water alone, and aquaglyceroporins are accepted as carrying water and small uncharged solutes including glycerol. This review presents an expanded view of aquaporins as channels with more complex mechanisms of regulation and diverse repertoires of substrate permeabilities than were originally appreciated in the early establishment of the field. The role of aquaporins as dual water and gated ion channels is likely to have physiological and potentially translational relevance, and can be evaluated with newly developed molecular and pharmacological tools. Ion channel activity has been shown for Aquaporins -0, -1, and -6, Drosphila Big Brain, and plant Nodulin-26. Although the concept of ion channel function in aquaporins remains controversial, research advances are beginning to define not only the ion channel function but also the detailed molecular mechanisms that govern and mediate the multifunctional capabilities. With regard to physiological relevance, the adaptive benefit of expression of ion channel activity in aquaporins, implied by amino acid sequence conservation of the ion channel gating domains, suggests they provide more than water or glycerol and solute transport. Dual ion and water channels are of interest for understanding the modulation of transmembrane fluid gradients, volume regulation, and possible signal transduction in tissues expressing classes of aquaporins that have the dual function capability. Other aquaporin classes might be found in future work to have ion channel activities, pending identification of the possible signaling pathways that could govern activation.

show abstract

“…It is specific for the lens and lens fibers, but its exact function in the tissue is not known. Recent hypotheses have proposed that MIP26 may have a number of different roles including function as a weak water channel (Chandy et al, 1997 ;Kushmerick et al, 1995 ;Mulders et al, 1995), a fiber cell adhesion protein (Costello, McIntosh and Robertson, 1989 ;Michea, de la Fuente and Lagos, 1994) and a nonselective ion channel (Ehring et al, 1990 ;Shen et al, 1991 ;Zampighi, Hall and Kreman, 1985). It has been known for some time that another lens membrane protein, MIP22 ; increases in abundance with age (Alcala, Valentine and Maisel, 1980 ;Horwitz et al, 1979 ;Roy, 1979 ;Roy, Spector and Farnsworth, 1979) and in a number of different experimental models for cataract.…”

Section: Introductionmentioning

confidence: 97%