what-when-how
In Depth Tutorials and Information
(A)
Collagen
Medium Cell layer
CIV-1CIV-1
Procollagen
Medium Cell layer
CIV-1CIV-1
[
α
1(III)]
3
pro
α
1(III)
pro
α
1(I)
pro
α
2(I)
α
1(I)
α
2(I)
(B)
1
0.8
Minutes chase
0 04060
120
Control
IV-1
Cell layer
Medium
0.6
0.4
Control
Cell layer
Medium
0.2
0
IV-1
0 04060
120
Minutes chase
FIGURE 16.3
Type I procollagen synthesis and secretion. (A) Labeling of cells with [3H]-proline for 16 hours showed normal synthesis and
secretion of type I procollagen into the culture medium and normal electrophoretic mobilities of the constituent chains. The chains of the pro-
collagens were separated under reducing conditions. The collagens represent the procollagens after digestion with pepsin and electrophoresis
under nonreducing conditions. (B) Cells were labeled for 1 hour with [3H]-proline then chased for up to 2 hours with unlabeled proline. The
secretion of the trimers of type I procollagen showed a delay in the rate of secretion in the patient cells, quantitated in the graph to the right.
26
Reprinted with permission of the publisher
.
These results are of interest in that while the over-
all rate of type I procollagen production was normal, in
the presence of HSP47 deficiency the triple-helical con-
formation of secreted type I collagen was altered so that
secreted type I collagen was protease sensitive at one
or more specific sites. Type III collagen secreted from
patient cells was also more protease sensitive, consistent
with a role for HSP47 in monitoring helix formation of
multiple collagen types. However, the HSP47 deficiency
did not appear to lead to delayed electrophoretic migra-
tion of the secreted pro-alpha chains of type I procolla-
gen considered to be an indicator of post-translational
overmodification.
points of triple-helical contact with a presumed result
that would depend on the specific mutations alter-
ing the type I collagen structure. In OI, mutations affect
both sides of the equation: first, due to alterations the
structure of the type I collagen triple helix, and second,
as reported by Christiansen et al., due to the HSP47 mol-
ecule itself. This chapter described one such mutation in
a patient with severe OI who succumbed to the disease.
The chapter also highlighted the probably extensive
variation in phenotype that can be expected as additional
mutations are discovered both in HSP47 and in the type I
collagen molecule.
References
SUMMARY
Mutations affecting the collagen chaperone protein
HSP47 lead to a recessively inherited skeletal pheno-
type consistent with moderately severe OI. This has been
demonstrated in dachshunds and in one Saudi Arabian
family. Undoubtedly other cases will be reported. Studies
to date detail the effects of mutations in HSP47 on its
binding to type I collagen primarily at the N-terminal
domain. However, the studies also suggest multiple
