Biomedical Engineering Reference
In-Depth Information
bilizing hydrogen bonds with its partner on the opposite strand only in the
staggered conformation [61]. In addition, they have also described a clever
synthetic method for introducing kinks and branches into fibrils [66, 67].
3.1.2
Nanofibrils from
β
-strands
We have studied sequences that form helical and sheet structures by in-
corporating specific interactions within a peptide sequence that would sta-
bilize both sheet and helix formation [18]. In these sequences, such as
DADADADARARARARA, a preformed
β
-sheet could be induced to adopt
a
-helix in response to temperature and pH changes. Other groups have also
studied this structural plasticity [45, 68]. In addition, investigators laid out
a carefully reasoned strategy for the design of short hexapeptide sequences
(i.e. KTVIIE, STVIIE, KTVIIT and KTVLIE) in order to test sequence elem-
ents critical for the formation of cross
α
β
-sheet structures and further test how
polymeric
-sheets can mature into amyloid fibrils [69]. Towards this goal it
is important to know how the cross
β
-sheet aggregates form and its role in
neurodegenerative disease; recent efforts in the de novo design of peptide-
based amyloid fibrils have aimed to identify simple sequences that minimally
satisfy the requirements of fibril formation [69, 70].
β
3.2
Bionanotubes and Vesicles
These amphiphilic molecules readily interact with water and form various
semi-enclosed environments. One of the best examples are phospholipids,
the predominant constituents of the plasma membrane, which encapsulate
and protect the cellular contents from the environment and are an abso-
lute prerequisite for almost all living systems. Phospholipids readily undergo
self-assembly in aqueous solution to form distinct structures that include mi-
celles, vesicles and tubules. This is largely a result of the hydrophobic forces
that drive the non-polar region of each molecule away from water and toward
one another.
3.2.1
Short Amphiphilic Peptides
Our laboratory has designed a simple peptide system with those proper-
ties [52, 53]. We made short peptides of around six to seven amino acids that
had the properties of surfactant molecules in that each monomer contained
a polar and a non-polar region. For example, a peptide called A6D, the pep-
tide molecule looked like a phospholipid in that it had a polar head group and
anon-polartail.
