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Figure 2.
Fig. 2. The pre-BCR CDR3-H sensing site. (A) Surface
representation of the pre-BCR structure in the same orientation
as shown in Fig. 1B. The VpreB unique region exits out the top
of the domain, lying over the HC antigen-combining site. (B)
Contact residues (29) within the SLC/HC interface zoomed into
the region demarcated by the red dashed box in (A). The main
chain is depicted as ribbons with contact residue side chains as
sticks. SLC, red; HC, blue. Asterisk designates the interchain
salt bridge between VpreB and HC. (C) At left, the CDR3-H (blue
sticks) from the HC on the surface of the VpreB/  5
segment of the SLC, showing the extent of interactions between
CDR3-H and the VpreB/ 5. The contact
footprint between CDR3-H and SLC is highlighted in red. To the
right, a similar projection of the CDR3-H on the surface of the
LC of a Fab. The contact footprint between CDR3-H and LC is
highlighted in red. The CDR3-H sequence is added below both
structures with the region shown in sticks highlighted (blue
letters). (D) Residues demarcating the human pre-BCR CDR3-H
sensing site. CDR3-H with side chains (blue), 5
(magenta), and VpreB (yellow) are shown. Pre-BCR side chains
that vary between human and mice and contact CDR3-H are shown in
cyan. The dashed line indicates a hydrogen bond. Below the
structure, a table of amino acid differences between mice and
humans in the region of the CDR3-H sensing site is appended.
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