Skip to main content
. 2019 Dec 9;8:e51409. doi: 10.7554/eLife.51409

Figure 2. Architecture of the β4 subunit.

(A) Stereo view of the β4 subunit monomer in ribbon representation with the extracellular side up. The N-terminal loop (‘N-loop’), TM1, extracellular domain (‘EC’) and TM2 are discretely colored gray, cyan, pink and blue. The gray bars delimit the membrane boundaries. (B) TM1 and TM2 within one β4 subunit interact extensively with each other. TM1 and TM2 are shown as ribbons in stereo view. Residues involved in the interactions are shown in sticks and colored according to atom type. (C) The EC domain of β4 subunit in stereo, viewed parallel to the membrane. The protein is shown as ribbons and colored as in panel (A). Four disulfide bonds and 2 N-glycosylation sugar groups are shown as sticks and colored according to atom type. (D, E) The β4 subunit tetramer in ribbon representation viewed parallel to the membrane (D) or from the extracellular side (E). Interfaces between two neighboring EC domains are highlighted by dotted circles. (F, G) The interface between the EC domain of two neighboring β4 subunits viewed parallel to the membrane (F) or from the extracellular side (G). The two EC domains are colored blue and pink. Sidechains of residues at the interface are shown as sticks and colored according to atom type.

Figure 2.

Figure 2—figure supplement 1. Sequence alignments.

Figure 2—figure supplement 1.

(A) Sequence alignment of the β subunit family. Secondary structures based on the cryo-EM structure of β4 are represented by ribbons (α helices), arrows (β strands), and lines (loops). Residues of the β4 subunit not modeled in the cryo-EM structure are denoted by dash lines. The four pairs of cysteine residues forming disulfide bonds are highlighted with color pairs. The two N-glycosylation sites are also highlighted in boxes. (B) Sequence alignment of the S0 helix of human Slo1 and human Slo3. Residues involved in Slo1-β4 association either through lipids or directly are highlighted purple and red, respectively. The corresponding residues conserved in Slo3 are underlined. (C) Sequence alignment of the two pore blocking toxins of human Slo1: CTX and IbTX, highlighting the basic residues.