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The results for this protein are shown in Figure 4.5. HingeMaster makes a strong
prediction for a hinge at residue 332 (StoneHinge TLSMD, hNMb, and hNMd in
agreement). This chain location does not appear in the HAG, but a search of the literature
uncovered evidence for a hinge at this location. Lactoferrin is organized into two
homologous halves, named the N and C lobes. Each of these lobes is further subdivided
into two domains: N1 and N2 in the N lobe and C1 and C2 in the C lobe. The opening of
these domains exposes an iron binding site in each lobe. The motion selected for Hinge
Atlas Gold shows the N1 domain (in blue) rotating relative to the rest of the molecule
exposing the binding site in the N-lobe. Thus, the HAG hinges are located between the
N1 and N2 domains. The hinge most strongly predicted by Hinge Master, however, falls
in between the C1 and N2 lobes and contributes to the movement of the two lobes
relative to each other. As in the case of Troponin C, experimental evidence is found for
this hinge, as lactoferrin crystals grown at 277 and 303 K show rotation between the two
lobes (Karthikeyan et al).
None of the predictive measures identify a hinge point at 90/91 in the open form
structure. However TLSMD analysis of the closed form of the same protein (PDB entry
1LFH; Morph ID f964705-18231) finds segment boundaries at 91/92 and 249/250 for the
3-segment partition, corresponding exactly to the lactoferrin mobile domain boundaries
(not shown).
Discussion
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