Nice thx! Hopefully ‘interesting’ in a good way 😝

these pics are very Harry Potter coded...

thanks for keeping us updated Ishier! Very nice introduction to Sean's talk... I especially thought the part about rafts was well put.

In summary:
1. sec24D, but not A, ERES are enriched in cholesterol.
2. sec24D ER exit sites sort raft-preferring proteins for fast ER efflux

Credit to Shikha Dagar, Rossana Ippolito, and ESPECIALLY Ivan Castello-Serrano who continued this work despite my skepticism until the data convinced me ;-)

Inhibiting raft lipids by myriocin (block sphingolipids) and zaragozic acid (blocks chol) disrupts sec24D ER exit sites and eliminates the fast ER efflux of raft-preferring protein

8/9

similarly, a fluorescent cholesterol (TF-Chol) accumulates in sec24D- but not in sec24A-positive ER exit sites (ERES)

7/9

sec24A versus sec24D isoforms recruit proteins differentially, based on the raft affinity of the cargo

6/9

How is this possible? Perhaps they are recognized by different cargo receptors?
- sec24A versus D isoforms are differently distributed within the cell
- sec24D puncta are largely near Golgi, sec24A are distributed throughout cytoplasm

5/9

- we used the Retention Using Selection Hook (RUSH) system to synchronize ER export of our favorite proteins: identical proteins with different single-pass transmembrane domains (TMDs) that determine raft affinity
- raft versus non-raft TMDs leave the ER at STRIKINGLY different rates
4/9

Big questions:

1. Cholesterol is synthesized in the ER but then exported… is there enough remaining to make raft domains?
2. sec24, the inner coat component of COP-II machinery in charge of cargo recognition, has 4 isoforms in mammals. Do they have non-overlapping functions? How?

3/9

1. determinants of cellular location for many proteins are unknown
2. lipid rafts are implicated in post-Golgi traffic, but not early secretory (ER)
3. cholesterol, critical for lipid rafts, is low in ER
4. adaptors that help cargo exit ER (sec24) have four isoforms, some prefer raft proteins

2/9