Interesting Gert. I took a look at the LRO Quickmap, and moved the map around at different angles to observe the terrain. As John says, this appears to be a valley or channel of sorts, but it is extremely worn, and is not at all obvious, even when looking at satellite images. I had to click on the option for "big shadows" on the LRO map in order to fully appreciate what is going on here. There are a collection of several features, which all work together to cause this effect, and your image happens to be at the exact right time for all of these to be working in concert.
The feature seems to begin with the shadowed region of the northern rim of Fabricius, on the border with Metius. It then progresses to the west, where it is bounded on the southern side initially by a raised portion of the outer terraced rim of Fabricius, and then by less obvious rolling terrain including the two worn craters that John mentioned. On the northern side, the feature appears to be bounded by the rampart separating Fabricius and Metius, and then by the worn craters, and finally by the southern rim of the crater Brenner A. It then continues for a bit, as seen in your image, being outlined by the southern rim of Brenner. None of these features is very impressive individually, but with the right lighting, they do indeed appear to make a valley of sorts.
Here is a figure I made from a few of the LRO images I used to look at the region. The white arrows point to the feature, although the regions that are apparent at any given time will depend on the sun angle. Note that the northern boundary is much better defined than the southern one.